Transistors having dynamically adjustable characteristics

ABSTRACT

Several inventions are disclosed. A cell architecture using hexagonal shaped cells is disclosed. The architecture is not limited to hexagonal shaped cells. Cells may be defined by clusters of two or more hexagons, by triangles, by parallelograms, and by other polygons enabling a variety of cell shapes to be accommodated. Polydirectional non-orthogonal three layer metal routing is disclosed. The architecture may be combined with the tri-directional routing for a particularly advantageous design. In the tri-directional routing arraingement, electrical conductors for interconnecting terminals of microelectronic cells of an integrated circuit preferrably extend in three directions that are angularly displaced from each other by 60°. The conductors that extend in the three directions are preferrably formed in three different layers. A method of minimizing wire length in a semiconductor device is disclosed. A method of minimizing intermetal capacitance in a semiconductor device is disclosed. A novel device called a &#34;tri-ister&#34; is disclosed. Triangular devices are disclosed, including triangular NAND gates, triangular AND gates, and triangular OR gates. A triangular op amp and triode are disclosed. A triangular sense amplifier is disclosed. A DRAM memory array and an SRAM memory array, based upon triangular or parallelogram shaped cells, are disclosed, including a method of interconnecting such arrays. A programmable variable drive transistor is disclosed. CAD algorithms and methods are disclosed for designing and making semiconductor devices, which are particularly applicable to the disclosed architecture and tri-directional three metal layer routing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/333,367, filed Nov. 2, 1994, by Ranko Scepanovic, et al., entitled"MICROELECTRONIC INTEGRATED CIRCUIT STRUCTURE AND METHOD USING THREEDIRECTIONAL INTERCONNECT ROUTING BASED ON HEXAGONAL GEOMETRY," theentire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This specification discloses a plurality of inventions relatinggenerally to the art of microelectronic integrated circuits andelectronic systems incorporating such circuits, and the disclosedsubject matter may be specifically applied to microelectronicsemiconductor integrated circuit structures and methods of designing andmanufacturing semiconductor devices.

BACKGROUND OF THE DISCLOSURE

The fabrication of semiconductor devices has progressed significantlyover the last four decades. Semiconductor chips incorporating over amillion transistors are possible. However, the development oftechnologies such as interactive high-definition television, personalglobal communications systems, virtual reality applications, real-lifegraphics animation, and other scientific and industrial applications,will demand higher speed, more functionality, and further advances invery large scale integration technology. The demand for morefunctionality will require an increase in the number of transistors thatneed to be integrated on a chip. This will require shrinking the arearequired to fabricate interconnected transistors, or will require largerdie sizes, or both. As the feature size decreases, and the area requiredto fabricate transistors decreases, the resulting increased density ofdevices will require an increasing number of interconnections within achip, or interconnections between chips in a multi-chip design.

Transistors or gates typically make up a circuit cell. Each cell of anintegrated circuit includes a plurality of points, sometimes referred toas pins or terminals, each of which must be connected to pins of othercells by an electrical interconnect wire network or net. Cells maycomprise individual logic gates, or more preferably may each comprise aplurality of logic gates or transistors that are interconnected to formfunctional blocks. It is desirable to attempt to optimize a design sothat the total wirelength and interconnect congestion are minimized.

As the number of transistors on a single chip becomes very large, gainsmade in reducing the feature size brought on by advances in fabricationtechnology may be offset by the increased area required forinterconnection. As the number of interconnections increase, the amountof real estate on the semiconductor die occupied by interconnectionscould become relatively large unless steps are taken to improveconventional layout techniques.

It is desirable to achieve minimum area layouts for very large scaleintegration circuits, because minimum area layouts typically deliveroptimum performance and provide the most economical implementation of acircuit. It is therefore desirable to have an architecture that willminimize the area occupied by the active part of the circuit. Forexample, an architecture that will tile well may provide advantages inminimizing the area occupied by the active part of the circuit. It isalso desirable to have an architecture that will minimize the areaoccupied by the passive part of the circuit, i.e., the interconnection.This may be achieved by an architecture that provides better routingoptions. Ultimately, the theoretical lower limit on minimizing the areaoccupied by the interconnections is a zero-routing footprint chip.

In the early days of large scale integration, only a single layer ofmetal was available for routing, and polysilicon (polycrystallinesilicon) and a single such metal layer were used to complete theinterconnections. The first metal layer may be referred to as the "metal1" layer or "M1" layer. As semiconductor fabrication processes improved,a second metal layer was added. The second metal layer may be referredto as the "metal 2" layer or "M2" layer. A rectangular approach torouting was used to determine the location of interconnections.Fabrication processes have now been developed which provide three orfour metal layers. Fabrication processes which provide five or moremetal layers are also being developed. Conductors can be formed inlayers that are electrically insulated from the cells and extend overthe cells, in what is sometimes referred to as over-the-cell routing.With three or four metal layers available for routing, it may bepossible to approach a chip containing no area set aside exclusively forrouting (i.e., a zero-routing footprint chip) if over-the-cell routingis utilized.

The performance of a chip depends on the maximum wire length of theinterconnection metal used. For better performance, it is desirable tominimize the maximum wire length. As the feature size is made smaller,the delay per unit length of interconnection increases. According to onereference, a 7 micron NMOS technology may have a per unit resistance of21 ohms per centimeter; and by comparison, a 0.35 micron CMOS technologymay have a per unit resistance of 2440 ohms per centimeter. See N.Sherwani, S. Bhingarde & A. Panyam, Routing in the Third Dimension, at 8(1995), the entirety of which is incorporated herein by reference.

The performance of a chip is bound by the time required for computationby the logic devices and the time required for the data communication.In the past, the time required for data communication was typicallyinsignificant compared to the time required for computation, and couldbe neglected. In the past three decades, there has been a significantimprovement in the average speed of computation time per gate. Now, theinterconnection delays are on the order of gate delays and as a result,have become significant and can no longer be ignored. Interconnectdelays are an increasing percentage of path delay.

When two points are interconnected by metal, a connection is formedwhich may be referred to as a wire. When two wires in the same metallayer run parallel to each other, parasitic capacitances may besignificant and "crosstalk" may occur between signals on those wires.The metal 1 layer is typically separated from the metal 2 layer by adielectric. When only two metal layers were used, a rectangular orrectilinear approach to routing provided metal 1 wires at 90 degreesrelative to metal 2 wires, and this gave satisfactory results in manyinstances. However, a rectangular approach to routing when three metallayers are available has provided metal 3 wires parallel to metal 1wires, and these metal layers are separated by layers of dielectric.This has resulted in unsatisfactory capacitance and "crosstalk" in manyinstances. With four metal layers, metal layers M1 and M3 may haveparallel wires, and metal layers M2 and M4 may have parallel wires.Significant performance degradation may result. In the past, efforts toincrease the number of metal layers in an attempt to approach azero-routing footprint chip have resulted in offsetting performancedegradation due to unsatisfactory capacitance and "crosstalk" fromparallel wires located in different metal layers.

Microelectronic integrated circuits consist of a large number ofelectronic components that are fabricated by layering several differentmaterials on a silicon base or wafer. The design of an integratedcircuit transforms a circuit description into a geometric descriptionwhich is known as a layout. A layout consists of a set of planargeometric shapes in several layers.

Typically, the layout is then checked to ensure that it meets all of thedesign requirements. The result is a set of design files in a particularunambiguous representation known as an intermediate form that describesthe layout. The design files are then converted into pattern generatorfiles that are used to produce patterns by an optical or electron beampattern generator that are called masks.

During fabrication, these masks are used to pattern a silicon waferusing a sequence of photolithographic steps. This component formationrequires very exacting details about geometric patterns and separationbetween them. These details are expressed by a complex set of designrules. The process of converting the specifications of an electricalcircuit into a layout is called the physical design. It is an extremelytedious and an error-prone process because of the tight tolerancerequirements, the complexity of the design rules, and the minuteness ofthe individual components.

Currently, the geometric feature size of a component may be as small ason the order of 0.5 microns. However, it is expected that the featuresize can be reduced to 0.1 micron within several years. This smallfeature size allows fabrication of as many as 4.5 million transistors or1 million gates of logic on a 25 millimeter by 25 millimeter chip. Thistrend is expected to continue, with even smaller feature geometries andmore circuit elements on an integrated circuit, and of course, largerdie (or chip) sizes will allow far greater numbers of circuit elements.

As stated above, each microelectronic circuit cell includes a pluralityof pins or terminals, each of which must be connected to pins of othercells by a respective electrical interconnect wire network or net. Agoal of the optimization process is to determine a cell placement suchthat all of the required interconnects can be made, and the totalwirelength and interconnect congestion are minimized. A goal of routingis to minimize the total wirelength of the interconnects, and also tominimize routing congestion. Achievement of this goal is restrictedusing conventional rectilinear routing because diagonal connections arenot possible. Rarely are points to be connected located in positionsrelative to each other such that a single straight wire segment can beused to interconnect the points. Typically, a series of wire segmentsextending in orthogonal directions have been used to interconnectpoints. A diagonal path between two terminals is shorter than tworectilinear orthogonal paths that would be required to accomplish thesame connection. Another drawback of conventional rectilinearinterconnect routing is its sensitivity to parasitic capacitance. Sincemany conductors run in the same direction in parallel with each other,adjacent conductors form parasitic capacitances that can create signalcrosstalk and other undesirable effects.

Conventional memory arrays such as DRAMs and SRAMs have been densitylimited by the metal pitch, which has become a limiting featureinhibiting further shrinkage of the size of the layout. In aconventional two layer memory array, the bit lines and the select linesnormally run on the same level of metal. As a result, as memory layoutsare made smaller and smaller, the bit lines and the select lines becomeclosely packed. Wiring congestion, crosstalk, and parasitic capacitanceare problems limiting the performance and size of conventional memoryarrays.

In the case of a DRAM cell, in particular, the line capacitance can be aproblem when it becomes large relative to the storage capacitance of thecell storage devices. A DRAM memory circuit can only tolerate a certainratio of line capacitance to storage capacitance. Conventional designsare limited in the available options to deal with this problem. Attemptshave been made to adjust the ratio of storage capacitance to linecapacitance by increasing the storage capacitance. However, increasingthe cell size tends to increase the size of the layout on a die, andlimits the amount of circuitry that can be laid out on a given size die,and may inflict performance penalties. Large amounts of storagecapacitance may slow the speed of a memory array. Large amounts ofcapacitance take longer to charge and discharge because largercapacitance has larger RC time constants. This slows the operation ofthe memory circuit. The speed of microprocessors and other circuits hasbecome so fast that memory accesses can be a significant limitation uponthe performance of a system where access speeds measured in nanosecondsare considered to be slow. Thus, increased capacitance can be a problemwith high performance memory circuits.

As illustrated in FIG. 1, a conventional microelectronic integratedcircuit 93 comprises a substrate 95 on which a large number ofsemiconductor devices are formed. These devices include large functionalmacroblocks such as indicated at 94 which may be central processingunits, input-output devices or the like. Many designers have a celllibrary consisting of standardized cells that perform desired logicaloperations, and which may be combined with other cells to form anintegrated circuit having the desired functionality. A typicalintegrated circuit further comprises a large number of smaller devicessuch as logic gates 96 which are arranged in a generally rectangularpattern in the areas of the substrate 95 that are not occupied bymacroblocks.

The logic gates 96 have terminals 98 to provide interconnections toother gates 96 on the substrate 95. Interconnections are made viavertical electrical conductors 97 and horizontal electrical conductors99 that extend between the terminals 98 of the gates 96 in such a manneras to achieve the interconnections required by the netlist of theintegrated circuit 93. It will be noted that only a few of the elements96, 98, 97 and 99 are designated by reference numerals for clarity ofillustration.

In conventional integrated circuit design, the electrical conductors 97and 99 are formed in vertical and horizontal routing channels (notdesignated) in a rectilinear (Manhattan) pattern. Thus, only twodirections for interconnect rouging are provided, although severallayers of conductors extending in the two orthogonal directions may beprovided to increase the space available for routing.

A goal of routing is to minimize the total wirelength of theinterconnects, and also to minimize routing congestion. Achievement ofthis goal is restricted using conventional rectilinear routing becausediagonal connections are not possible. A diagonal path between twoterminals is shorter than two rectilinear orthogonal paths that would berequired to accomplish the same connection.

Another drawback of conventional rectilinear interconnect routing is itssensitivity to parasitic capacitance. Since many conductors run in thesame direction in parallel with each other, adjacent conductors formparasitic capacitances that can create signal crosstalk and otherundesirable effect.

Other patents exist which contain incidental references to hexagonalstructures, but do not disclose the hexagonal architecture of thepresent invention. For example, U.S. Pat. No. 5,323,036 purports todisclose a power FET transistor that has gate segments arranged in ahexagonal lattice pattern in an effort to reduce channel resistance.U.S. Pat. No. 5,323,036 does not teach or suggest providing three metallayers in a hexagonal architecture as provided by the present invention.Significantly, that patent does not even recognize the problem ofminimizing interconnection wire lengths and interlayer capacitance or"crosstalk."

U.S. Pat. No. 5,095,343 purports to disclose a VDMOS device havingP-type regions forming PN junctions that intersect the surface of thewafer in a closed path forming a hexagon along the plane of the surface.Each source region is stated to be opposite the space between two sourceregions in the adjacent body region. This is said to provide each cellwith a plurality of spaced channel regions. According to this patent,the disclosed VDMOS device has a reduced power density at which zerotemperature coefficient occurs so that the device allegedly can toleratea given power dissipation for a longer time before damage occurs. U.S.Pat. No. 5,095,343 may teach away from over-the-cell routing; the patentdescribes a metal connection to the gate electrode, and states that thegate bond pad overlies an area of the surface of the wafer that does notcontain source/body cells. This patent does not teach or suggestproviding three metal layers in a hexagonal architecture preferablyemploying over-the-cell routing, and does not recognize the problem ofminimizing interconnection wire lengths and interlayer capacitance or"crosstalk."

U.S. Pat. No. 5,130,767 purports to disclose a high power MOSFETtransistor that has a plurality of closely packed polygonal sourcesspaced from one another on one surface of a semiconductor wafer. Thepatent states that the polygonal source regions are preferably hexagonalin shape. A single drain electrode is formed on the opposite surface ofthe semiconductor wafer. An elongated gate electrode is formed on thefirst surface of the wafer and it crosses a plurality of the polygonalsources. When a suitable control voltage is applied to the gate, annularchannels around the polygonal sources become conductive to permitmajority carrier conduction from the source regions through the wafer tothe drain electrode on the opposite surface of the wafer. U.S. Pat. No.5,130,767 does not teach or suggest providing three metal layers in ahexagonal architecture, and does not recognize the problem of minimizinginterconnection wire lengths and interlayer "crosstalk."

While in the past satisfactory results were obtained using rectangulararchitectures employing two layers of metal, those old techniques willnot suffice for many new designs incorporating millions of transistors.As very large scale integration designs advance, and attempts are madeto place more and more transistors on the same area of a semiconductorchip, improved architectures are needed to provide minimal area designsand better performance. The techniques and architectures used in thepast leave considerable room for improvement.

SUMMARY OF THE INVENTIONS

Several inventions are disclosed herein. In the course of thedescription that follows, the discussion may at various times refer to"the present invention." Such a reference is not intended to imply thatonly one invention is disclosed, but may refer in context to theparticular subject matter then being described by way of example andwithout limitation of the scope of all of the inventions that aredisclosed through out the present specification.

For example, a cell architecture using hexagonal shaped cells isdisclosed. The architecture is not limited to hexagonal shaped cells.Cells may be defined by clusters of two or more hexagons, by triangles,by parallelograms, and by other polygons enabling a variety of cellshapes to be accommodated. Polydirectional non-orthogonal three layermetal routing is disclosed. The architecture may be combined with thetri-directional routing for a particularly advantageous design. A methodof minimizing wire length in a semiconductor device is disclosed. Amethod of minimizing intermetal capacitance in a semiconductor device isdisclosed. A novel device called a "tri-ister" is disclosed. Triangulardevices are disclosed, including triangular NAND gates, triangular ANDgates, and triangular OR gates. A triangular op amp and triode aredisclosed. A triangular sense amplifier is disclosed. A DRAM memoryarray and an SRAM memory array, based upon triangular or parallelogramshaped cells, are disclosed, including a method of interconnecting sucharrays. A programmable variable drive transistor is disclosed. CADalgorithms and methods are disclosed for designing and makingsemiconductor devices, which are particularly applicable to thedisclosed architecture and tri-directional three metal layer routing.

In accordance with one aspect of the present invention, three layers ofmetal provide electrical conductors for interconnection which extend inthree directions that are angularly displaced from each other by 60degrees, which is sometimes referred to as a tri-directional orhexagonal routing system. This is the preferred embodiment of thepolydirectional non-orthogonal three layer metal routing invention. Onaverage, the three direction routing system according to one aspect ofthe present invention using three metal layers for interconnect willresult in a total interconnect wire length that is shorter than thetotal interconnect wire length required using a conventional two metallayer rectangular routing system. This tri-directional routing can beused in connection with conventional rectangular cells, or it may beadvantageously used in conjunction with triangular, hexagonal, diamond,parallelogram shaped cells, as well as any other arbitrary shaped cell.

The three routing directions provided by the present inventionsubstantially reduce the total wirelength interconnect congestion of anintegrated circuit. The routing directions include, relative to a firstdirection, two diagonal directions that provide shorter interconnectpaths than conventional rectilinear routing.

In addition, the number of conductors that extend parallel to each otheris smaller, and the angles between conductors in different layers arelarger than in the prior art, thereby reducing parasitic capacitance andother undesirable effects that result from conventional rectilinearrouting.

In accordance with another aspect of the present invention, aprogrammable design of a substrate having a plurality of partiallyprefabricated transistors, sometimes referred to as incohatetransistors, which may be finally constructed to have a range of desiredsizes, drive currents, or delays, where transistors are fabricated froma triangular transistor design and the location of the gate electrodesmay be adjusted during final fabrication.

One embodiment includes a microelectronic integrated circuit that mayadvantageously utilize the three direction routing arrangement describedherein. A triangular device design includes a semiconductor substrate,and a plurality of microelectronic devices that are formed on thesubstrate in a closely packed triangular arrangement that maximizes thespace utilization of the circuit.

Each device has a periphery defined by a large triangle, and includes anactive area formed within the periphery. First and second terminals areformed in the active area adjacent to two vertices of the trianglerespectively, and first to third gates are formed between the first andsecond terminals.

The gates have contacts formed outside the active area adjacent to aside of the triangle between the two vertices. The first and secondterminals, and the gates are preferrably connected using the threedirection (or tri-direction) hexagonal routing arrangement, althoughrectilinear routing may also be used.

The power supply connections to the central terminal and the first tothird terminals, the conductivity type (NMOS or PMOS), and the additionof a pull-up or a pull-down resistor may be selected for each device toprovide a desired AND, NAND, OR or NOR function. A third terminal can beformed between two of the gates and used as an output terminal toprovide an AND/OR logic function.

In accordance with another aspect of the present invention, anintegrated circuit includes a semiconductor substrate, and a pluralityof CMOS microelectronic devices formed on the substrate. Each deviceincludes a triangular ANY element of a first conductivity type (PMOS orNMOS), and a triangular ALL element of a second conductivity type (NMOSor PMOS), the ANY and ALL elements each having a plurality of inputs andan output that are electrically interconnected respectively.

The ANY element is basically an OR element, and the ALL element isbasically an AND element. However, the power supply connections and theselection of conductivity type (NMOS or PMOS) for the ANY and ALLelements can be varied to provide the device as having a desired NAND,AND, NOR or OR configuration, in which the ANY element acts as a pull-upand the ALL element acts as a pull-down, or vice-versa.

A triangular OR gate device is provided in accordance with one aspect ofthe present invention. First to third gates are formed between the firstto third terminals, respectively, and the central terminal, and havecontacts formed outside the active area adjacent to the edges of thetriangle. The central and first to third terminals, and the gates arepreferrably connected using the three direction hexagonal routingarrangement.

The power supply connections to the central terminal and the first tothird terminals, the conductivity type (NMOS or PMOS), and the additionof a pull-up or a pull-down resistor is selected for an illustratedtriangular device to provide a desired OR function. One or two of thefirst to third terminals, rather than the central terminal, can be usedfor output to provide an AND/OR logic function.

Conductors that extend in the three directions can be formed in threedifferent layers, or alternatively the conductors that extend in two orthree of the directions can be formed in a single layer as long as theydo not cross. The conductors can be formed in layers that areelectrically insulated from the cells and extend over the cells, or canextend through hexagons between cells. Conductors may be provided thatextend in three directions that form an acute angle relative to eachother. In another alternative form of the invention, additionalconductors can be added that extend in a direction perpendicular to oneof the other three directions.

Cells can have serrated edges defined by edges of hexagons such thatadjacent cells fit together exactly, providing a closely packedarrangement of cells on the substrate with effective utilization ofspace. Cells can be defined by clusters of two or more hexagons,enabling a variety of cell shapes to be accommodated. Sets of cellshaving the same functionality and different shapes may be provided.

These and other features and advantages of the present inventions willbe apparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings, in whichlike reference numerals refer to like items.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a prior art integrated circuit.

FIG. 2 is an exploded schematic diagram illustrating two layers ofmetal.

FIG. 3 is an exploded schematic diagram illustrating three layers ofmetal.

FIG. 4 is an exploded schematic diagram illustrating three layers ofmetal, where the layers of metal provide electrical conductors forinterconnection which extend in three directions that are angularlydisplaced from each other by 60 degrees.

FIG. 5 is a diagram illustrating examples of unit circle routing lengthfor a rectangular routing system having two directions ("X" and "Y") ascompared to a hexagonal routing system having three directions ("A," "B"and "C").

FIG. 6 is a bar graph depicting average extra unit circle routing lengthvs. the number of wiring layers, using a direct radial connection (i.e.,unity) as a basis for comparison.

FIG. 7 is a bar graph depicting percent improvement in average extraunit circle routing length vs. the number of wiring layers using twowiring layers as the basis of comparison.

FIG. 8 is a diagram illustrating three direction routing forinterconnecting example devices based on hexagonal geometry inaccordance with the present invention.

FIG. 9 is a diagram illustrating one example device which is connectedusing the three direction routing of FIG. 8.

FIG. 10 is a diagram illustrating an example of an integrated circuitincluding a plurality of devices in a closely packed triangulararrangement.

FIG. 11 depicts a layout of hexagonal shaped cells on a semiconductorsubstrate.

FIG. 12 depicts a layout of hexagonal shaped cells on a semiconductorsubstrate having channels provided between cells to provide room forrouting.

FIG. 13 depicts a layout of a hexagonal shaped cell on a semiconductorsubstrate comprising six triangular shaped cells.

FIG. 14 is a top view of a triangular shaped transistor on asemiconductor substrate.

FIG. 15 is a top view of an alternative embodiment of a triangularshaped transistor on a semiconductor substrate.

FIG. 16 is a top view of another alternative embodiment of a triangularshaped transistor on a semiconductor substrate.

FIG. 17 depicts a layout of a plurality of hexagonal shaped cells on asemiconductor substrate each comprising six triangular shaped cells.

FIG. 18 depicts a layout of triangular shaped cells forming a largerdiamond shaped megafunction cell.

FIG. 19 depicts a layout of triangular shaped cells forming a largertriangular shaped megafunction cell.

FIG. 20 is a top view of an embodiment of a triangular shaped structurereferred to as a tri-ister comprising three transistors on asemiconductor substrate.

FIG. 20A is a top view of an alternative embodiment of a tri-ister.

FIG. 20B is a top view of an alternative embodiment of a tri-ister.

FIG. 20C is a top view of an alternative embodiment of a tri-ister.

FIG. 20D is a top view of an alternative embodiment of a tri-ister.

FIG. 21 is a top view of the layout of an SRAM cell on a semiconductorsubstrate.

FIG. 22 is a top view of the layout on a semiconductor substrate of analternative embodiment of a memory circuit comprising a plurality oftriangular shaped structures each comprising three transistors.

FIG. 22A is a schematic diagram of one cell of the memory circuitillustrated in FIG. 22.

FIG. 23 is a top view of the layout on a semiconductor substrate of anembodiment of a sense amplifier for an SRAM memory circuit comprising atriangular shaped structure comprising three transistors.

FIG. 23A is a schematic diagram of the sense amplifier illustrated inFIG. 22.

FIG. 23B depicts a layout of a triangular shaped DRAM cell.

FIG. 23C is a schematic diagram of the equivalent circuit for thetriangular DRAM cell shown in FIG. 23B.

FIG. 24 depicts a layout of one half of a double triangular shaped cell.

FIG. 25 depicts a layout of two triangular shaped structures forming adouble triangular shaped cell.

FIG. 26 depicts a layout of two triangular shaped structures forminganother type of double triangular shaped cell.

FIG. 27 depicts a layout of two triangular shaped structures forminganother type of double triangular shaped cell.

FIG. 28 depicts a layout of a plurality of triangular shaped structurescomprising the three types of double triangular shaped cells shown inFIG. 25, FIG. 26, and FIG. 27, forming a larger diamond shapedmegafunction cell.

FIG. 29 is a diagram of an area of a chip that is to be laid out usinghexagonal architecture which is used to illustrate the operation of aplacement algorithm.

FIG. 30 is a diagram of an area of a chip showing two hierachies ofhexagonals used in floor planning to illustrate the operation of aplacement algorithm.

FIG. 31 is a graph depicting routing density of one of the layers ofmetal in an example of a microelectronic device using two layerrectilinear routing.

FIG. 32 is a graph depicting routing density of the second layer ofmetal of the device referred to in connection with FIG. 31.

FIG. 33 is a graph depicting routing density of one of the layers ofmetal in another example of a microelectronic device using two layerrectilinear routing.

FIG. 34 is a graph depicting routing density of the second layer ofmetal of the device referred to in connection with FIG. 33.

FIG. 35 is a diagram illustrating possible routes available forinterconnection of example points to illustrate the operation of arouting algorithm.

FIG. 36 is a diagram illustrating a microelectronic gate device which isan example of one embodiment of the present invention.

FIG. 37 is an electrical schematic diagram illustrating the presentdevice connected to provide a logical AND function.

FIG. 38 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical NAND function.

FIG. 39 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical OR function.

FIG. 40 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical NOR function.

FIG. 41 is a diagram illustrating the gate device with alternative gateconnections.

FIG. 42 is a diagram illustrating one device as connected using thethree direction routing according to one aspect of the presentinvention.

FIG. 43 is a diagram illustrating a microelectronic integrated circuitincluding a plurality of the present gate devices in a closely packedtriangular arrangement.

FIG. 44 is a diagram illustrating the gate device connected to provide alogical AND/OR function.

FIG. 45 is a schematic diagram illustrating the logical functionality ofthe device connected as shown in FIG. 44.

FIG. 46 is a schematic diagram illustrating how individual field effecttransistors of the device are connected as shown in FIG. 44.

FIG. 47 is a diagram illustrating the gate device as having a modifiedgate configuration.

FIG. 48 is a diagram illustrating a microelectronic gate device which isan example of one embodiment of the present invention;

FIG. 49 is an electrical schematic diagram illustrating the presentdevice connected to provide a logical NAND function;

FIG. 50 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical AND function;

FIG. 51 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical NOR function;

FIG. 52 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical OR function;

FIG. 53 is a diagram illustrating the gate device connected to provide alogical NAND function with reversed source and drain connections;

FIG. 54 is a diagram illustrating the gate device connected to provide alogical AND/OR function;

FIG. 55 is a functional circuit diagram of the gate device of FIG. 54;and

FIG. 56 is a schematic diagram illustrating the gate device of FIG. 54as being represented by field-effect transistors.

FIG. 57 is a diagram illustrating a microelectronic gate deviceembodying the present invention;

FIG. 58 is an electrical schematic diagram illustrating the presentdevice connected to provide a logical OR function;

FIG. 59 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical NOR function;

FIG. 60 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical AND function;

FIG. 61 is an electrical schematic diagram illustrating the gate deviceconnected to provide a logical NAND function;

FIG. 62 is a diagram illustrating one device as connected using thethree direction routing of FIG. 8;

FIG. 63 is a diagram illustrating a microelectronic integrated circuitincluding a plurality of the present gate devices in a closely packedtriangular arrangement;

FIG. 64 is a diagram illustrating the gate device connected to provide alogical OR function with source and drain connections reversed;

FIG. 65 is a diagram illustrating the gate device connected to provide alogical AND/OR function;

FIG. 66 is a schematic diagram illustrating the logical functionality ofthe device connected as shown in FIG. 65;

FIG. 67 is a schematic diagram illustrating how individual field effecttransistors of the device are connected as shown in FIG. 65;

FIG. 68 is a diagram illustrating a modification of the arrangementillustrated in FIG. 65.

FIG. 69 is a flow chart illustrating a placement algorithm.

FIG. 70 is a flow chart illustrating a routing algorithm.

FIG. 71 is a flow chart illustrating a portion of the routing algorithmin more detail.

FIG. 72 is a flow chart illustrating a portion of the routing algorithmin more detail.

FIG. 73 is a diagram illustrating a combination of three directionrouting with hexagonal geometry cells.

FIG. 74 is a diagram illustrating how a routing arrangement inaccordance with one aspect of the present inventions may producesubstantially 100% adjacent equidistant connectivity of cells.

FIG. 75 is a diagram illustrating a microelectronic integrated circuitaccording to one aspect of the present inventions in which electricalconductors extending in three directions are formed in a single layer.

FIG. 76 is a diagram illustrating how microelectronic cells of differentshapes and sizes can be accommodated using a tri-directional routingarrangement.

FIG. 77 is similar to FIG. 75, but illustrates an arrangement in whichelectrical conductors extend in two directions in one routing layer,whereas electrical conductors extend in a third direction in a secondrouting layer.

FIG. 78 is a diagram illustrating electrical conductors extending inthree directions in three routing layers respectively.

FIG. 79 is a diagram illustrating a square shaped cell formed in acluster of hexagons superimposed on a substrate in order to provide aplurality of terminals available for routing.

FIG. 80 is similar to FIG. 79, but illustrates a circular shaped cell.

FIG. 81 is also similar to FIG. 79, but illustrates a cell having anarbitrary irregular shape.

FIG. 82 is a diagram illustrating a microelectronic integrated circuitcomprising a plurality of cells, and electrical conductors extendingbetween the cells in two directions.

FIG. 83 is similar to FIG. 82, but illustrates electrical conductorsextending in three directions between the cells.

FIG. 84 is a diagram illustrating adjacency relationships in a prior artmicroelectronic integrated circuit arrangement.

FIG. 85 is similar to FIG. 85, but illustrates adjacency relationshipsin a microelectronic integrated circuit arrangement using hexagonalshaped cells.

FIG. 86 is a diagram illustrating a microelectronic integrated circuitcomprising cells defined by clusters of hexagons, with each cell havingfour serrated edges.

FIG. 87 is similar to FIG. 86, but illustrates cells having two serratededges and one or two straight edges.

FIG. 88 is also similar to FIG. 86, but illustrates cells havingirregular shapes with serrated edges.

FIG. 89 is a diagram illustrating closely packed hexagonal cells withterminals at centers of smaller hexagons disposed inside the cells.

FIG. 90 is a diagram illustrating a set of functionally similar cellshaving different edge shapes.

FIG. 91 illustrates an exemplary integrated circuit chip.

FIG. 92A shows a prior art block of near square or square sub blockcells.

FIG. 92B shows an exemplar prior art square of a near square block (orsub-block) of simple construction.

FIG. 93A shows a hexagonal block structure similar to a hex block shownin FIG. 91.

FIG. 93B shows an exemplar triangular block or sub-block.

FIG. 94 shows a near-hexagonal block comprised by triangular sub-blocksand having intersection angles θ, φ and Ω of the respective separatinglines at 60 degrees.

FIG. 95A shows a block composed of triangular sub-blocks, where thesub-block demarcation lines define right-triangles having demarcationline intersection angles θ and Ω of 60 degrees and φ of 90 degrees.

FIG. 95B shows an exemplar triangular block or sub-block.

FIG. 96A shows a block structure composed of parallelogram sub-blocks.

FIG. 96B shows an exemplar parallelogram block or sub-block.

FIG. 97A shows a block structure composed of rhomboidal blocks.

FIG. 97B shows a detailed schematic of an electronic circuit for anexemplar rhomboidal block or sub-block which could represent any one ofthe sub-blocks shown in FIG. 97A.

FIG. 98 is a flow chart depicting a process by which floorplanning maybe performed.

FIG. 99 is a flow chart showing a process of floorplanning incorporatingpartitioning for minimum aspect ratio sub-partitions.

FIG. 100 is a schematic block diagram of an integrated circuit andsystem which may incorporate the present invention.

FIG. 101 is a schematic block diagram of a digital system incorporatingthe present invention.

FIG. 102 is a schematic block diagram of a multiprocessor computersystem.

FIG. 103 is a schematic block diagram of a complex digital computersystem incorporating the present invention.

FIG. 104 is a schematic block diagram of a large scale integratedcircuit utilizing the present invention.

FIG. 105 is a schematic block diagram of a digital cellular telephonewhich may incorporate embodiments of the present invention.

FIG. 106 is a schematic block diagram of a digital home entertainmentsystem utilizing the present invention.

FIG. 107 is a perspective view of a schematic illustration of aconventional rectilinear routing design.

FIG. 108 shows a cross sectional view of the metal wires shown in FIG.107.

FIG. 109 shows another example of a cross sectional view of metal wiresin a conventional rectilinear routing design.

FIG. 110 is a perspective view of a schematic illustration of atri-directional routing example.

FIG. 111 is a perspective drawing illustrating a jumper connectorfabricated in the second metal layer to make an electrical connectionbetween two conductors in the third metal layer.

FIG. 112 illustrates a top view of an example of a layout for atri-ister structure.

FIG. 113 is a graph showing a main transistor voltage-current curves forthe tri-ister shown in FIG. 112.

FIG. 114 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 115 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 116 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 117 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 118 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 119 is a graph showing transistor characteristics for the maintransistor of the tri-ister shown in FIG. 112.

FIG. 120 shows a layout for two tri-isters configured as an invertercircuit.

FIG. 121 shows an inverter transfer curve for the structure depicted inFIG. 120 when V_(D1) and V_(D2) are floating.

FIG. 122 shows an inverter transfer curve for the structure depicted inFIG. 120 which is controlled by V_(D2).

FIG. 123 shows an inverter transfer curve for the structure depicted inFIG. 120 which is controlled by V_(D1).

FIG. 124A shows one example of a partial layout for an operationalamplifier.

FIG. 124B shows a schematic diagram of an equivalent circuit for thestructure depicted in FIG. 124A.

FIG. 124C shows a layout of an operational amplifier.

FIG. 125 shows a schematic diagram of a field programmable device.

FIG. 126 shows a top view of a layout for a field programmable device.

FIG. 127 shows an example of a hexagonal cell comprising six of thestructures shown in FIG. 126 arrainged in an array.

FIG. 128 illustrates a cross-sectional view of one embodiment of an E²PROM type field programmable device.

FIG. 129 is a cross-sectional view of an alternative embodiment of aDRAM type field programmable device.

FIG. 130 illustrates a top view of the layout of a quad-ister structure.

FIG. 131 shows a top view of three wire, each of which is in one ofthree layers of metal, and the wires are to be connected by a hexagonalshaped via.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTIONS

In FIG. 2, two conventional layers of metal are shown schematically.This is an exploded diagram separating the individual layers forclarity. A first metal (M1) layer 100 is shown separated from a secondmetal (M2) layer 101 by a dielectric layer 102. A conventionalrectangular routing arrangement is illustrated. The first metal layer100 provides for electrical connections in a direction that is angularlydisplaced 90 degrees from electrical connections provided by the secondmetal layer 101. For example, in the M1 layer 100, a point 103 isconnected to a point 104 by a metal wire 105. In the M2 layer 101, apoint 106 is connected to a point 107 by a metal wire 108. The wire 105is angularly displaced 90 degrees from the wire 108; in other words, thewire 105 in the M1 layer 100 is perpendicular to wire 108 in the M2layer 101. Wires in the same layer will be parallel to each other. Forexample, point 109 in the M1 metal layer 100 is connected to point 110by a wire 111. The wire 111 is parallel to the wire 105 in the same M1metal layer 100, and is perpendicular to the wire 108 in the M2 metallayer 101.

Using conventional interconnection such as that shown in FIG. 2, thedevice capacity of a die may be directly limited by the interconnection.Interconnection is a large factor in die processing costs.Interconnection can be a significant factor in chip yield. Therefore,better interconnection designs can offer significant advantages.

A better interconnection design is shown in FIG. 3, where three layersof metal are shown schematically. As was the case with FIG. 2, this isalso an exploded diagram showing the individual layers separated forclarity. The first metal (M1) layer 100 is shown separated from thesecond metal (M2) layer 101 by the dielectric layer 102. A third metal(M3) layer 112 is shown separated from the second metal (M2) layer 101by a dielectric layer 113. A conventional rectangular routingarrangement is illustrated. The first metal layer 100 provides forelectrical connections in a direction that is angularly displaced 90degrees from electrical connections provided by the second metal layer101. As described with reference to FIG. 2, a point 103 in the M1 layer100 is connected to a point 104 by a metal wire 105. In the M2 layer101, a point 106 is connected to a point 107 by a metal wire 108. Thewire 105 is angularly displaced 90 degrees from the wire 108. Wires inthe same layer are parallel to each other. As described with referenceto FIG. 2, point 109 in the M1 metal layer 100 is connected to point 110by the wire 111. The wire 111 is parallel to the wire 105 in the same M1metal layer 100, and is perpendicular to the wire 108 in the M2 metallayer 101.

The third metal layer 112 provides for electrical connections in adirection that is angularly displaced 90 degrees from electricalconnections provided by the second metal layer 101. A point 114 in theM3 layer 112 is connected to a point 115 by a metal wire 116. The wire116 is perpendicular to the wire 108 in the M2 metal layer 101. However,the third metal layer 112 provides for electrical connections in adirection that are parallel to electrical connections provided by thefirst metal layer 100. In other words, the first metal layer 100provides for electrical connections in a direction that is angularlydisplaced 0 degrees from electrical connections provided by the thirdmetal layer 112. This is a worst case orientation for parasiticcapacitance and crosstalk. Problems with parasitic capacitance may beaccentuated by the parallel orientation of the wires 116 in the M3 metallayer 112 with wires 105 in the M1 metal layer 100.

FIG. 4 shows three layers of metal schematically, with the metal routingdirections separated by 60 degree angles. As was the case with FIG. 2,this is also an exploded diagram showing the individual layers separatedfor clarity, but has been simplified by omitting dielectric layers. Afirst metal (M1) layer 117, a second metal (M2) layer 118, and a thirdmetal (M3) layer 118 are provided. The first metal (M1) layer 117 isseparated from the second metal (M2) layer 118 by a dielectric layer(not shown), and the second metal (M2) layer 118 is separated from thethird metal layer (M3) 119 by a dielectric layer (not shown).

Minimizing Total Wire Length Using Tri-Directional Routing

In accordance with the present invention, the three layers of metal 117,118, 119 provide electrical conductors for interconnection which extendin three directions that are angularly displaced from each other by 60degrees. For example, in the M1 metal layer 117, a point 120 isconnected to a point 121 by a wire 122, and a point 123 is connected toa point 124 by a wire 125. In the M2 metal layer 118, a point 126 isconnected to a point 127 by a wire 128. In the M3 metal layer 119, apoint 129 is connected to a point 130 by a wire 131. The wires 122 and125 in the M1 metal layer 117 are angularly displaced from wire 128 inthe M2 metal layer 118 by 60 degrees. The wires 122 and 125 in the M1metal layer 117 are also angularly displaced from wire 131 in the M3metal layer 119 by 60 degrees. And the wire 128 in the M2 metal layer118 is angularly displaced from the wire 131 in the M3 metal layer 119by 60 degrees.

The three degrees of freedom provided by the three layers of metal 117,118, and 119 should result in shorter total interconnection wirelengths. This may be better appreciated by considering a unit circlerouting length in connection with FIG. 5. If we consider the case of anarbitrary first point 132 selected for the sake of discussion which mustbe connected to a second point. For purposes of discussion, the secondpoint may be located at any arbitrary location relative to the firstpoint 132, which results in the first and second points being located atan angle with respect to each other. For this discussion, the relativeangle is of particular interest, so it will suffice if the second pointis considered to be located anywhere on a unit circle 133.

In FIG. 5, the conventional rectangular routing system uses two wiringdirections, shown as direction "X" and direction "Y" represented in theupper left of the Figure. The hexagonal routing system uses three wiringdirections, shown as direction "A," direction "B," and direction "C"represented in the upper right of FIG. 5. For simplicity, direction "A"is oriented the same as direction "X." If every point on the unit circle133 is considered, and the length of wire required to connect the pointsusing conventional rectangular routing compared with hexagonal routingis calculated, the average length of total interconnect wire required toconnect points which are located arbitrarily with respect to each othermay be computed.

For example, if the point 132 must be connected to a point 135 usingconventional rectangular routing, a wire 136 in the "X" directioncombined with a wire 137 in the "Y" direction must be used to make theconnection. However, if the point 132 must be connected to the point 135using hexagonal routing, a wire 138 in the "A" direction combined with awire 139 in the "B" direction may be used to make the connection. Thelength of the wire 138 plus the length of the wire 139 is shorter thanthe length of the wire 136 plus the length of the wire 137.

Similarly, if the point 132 must be connected to a point 143 usingconventional rectangular routing, a wire 144 in the "X" directioncombined with a wire 145 in the "Y" direction must be used to make theconnection. Using hexagonal routing, if the point 132 must be connectedto the point 143, a wire 146 in the "C" direction combined with a wire147 in the "B" direction may be used to make the connection. The lengthof the wire 146 plus the length of the wire 147 is shorter than thelength of the wire 144 plus the length of the wire 145. In the exampleof the connection of point 132 with a point 148 shown in FIG. 5, thelength of wire 149 and wire 150 using conventional rectangular routingis longer than the length of wire 151 and wire 152 using hexagonalrouting.

Some exception points do exist such as point 153 where the connectionusing rectangular routing only requires a single wire 155 in the "Y"direction. In this special case, the wire 155 is shorter than the wires157 and 159 required in the illustrated hexagonal routing system.

On average, the hexagonal routing system using three metal layers forinterconnect will result in a total interconnect wire length that isshorter than the total interconnect wire length required using aconventional two metal layer rectangular routing system. This is shownin FIG. 6. FIG. 6 is a bar graph depicting average extra unit circlerouting length vs. the number of wiring layers, using a direct radialconnection (i.e., unity) as a basis for comparison. An average extraunit circle routing length may be computed for the points located on aunit circle. The two metal layer example described above would have anaverage extra unit circle routing of about 0.27. The three metal layerexample described above would have an average extra unit circle routingof only about 0.10. The percent improvement in average unit circlelength over a conventional two metal layer rectangular routing system isshown in FIG. 7. The three metal layer example described above wouldhave a 13.4% improvement in the average extra unit circle routing ascompared to a conventional two metal layer rectangular routing system.

Increasing the number of metal layers to four or more provides adiminishing rate of return. This can be seen from FIG. 6 and FIG. 7.Four metal layers has an average extra unit circle routing length ofabout 0.05, which is about a 17.2% improvement over a conventional twometal layer rectangular routing system. Five metal layers has an averageextra unit circle routing length of about 0.03, which is about an 18.8%improvement over a conventional two metal layer rectangular routingsystem. Thus, only about 1.6 percentage points of improvement areachieved by going from four metal layers to five metal layers. FIG. 7shows that only about 0.2 percentage points of improvement are realizedin going from nine metal layers to ten metal layers.

An example of a geometry for a three directional routing arrangement forinterconnecting hexagonal cells fabricated on a semiconductor substrateis illustrated in FIG. 8. For purposes of comparison, an orthogonalcoordinate system is shown having an "x" axis and a "y" axis. A closelypacked pattern of small hexagon shaped cells 1300 is superimposed on thecoordinate system, with the centers of the hexagons 1300 beingdesignated as terminal points 1302.

For the purpose of the present disclosure, the term "closely packed" isconstrued to mean that the hexagons 1300 are formed in a contiguousarrangement with adjacent hexagons 1300 sharing common sides asillustrated, with substantially no spaces being provided betweenadjacent hexagons 1300. Devices based on the present hexagonalarchitecture may be formed on the substrate in a closely packedarrangement, with each device covering a number of the small hexagons1300. Application of the described routing arrangement is not limited tohexagonal devices. The hexagonal routing for interconnections describedherein may also be used with rectangular devices.

In accordance with the invention, the centers of the hexagons 1300 asindicated at 1302 may represent interconnect points for terminals of theillustrated devices. Electrical conductors for interconnecting thepoints 1302 may extend in three directions that make angles of 60°relative to each other.

The conductors that extend in the three directions are preferrablyformed in three different layers, with conductors in one direction beingformed on one and only one of the three layers of metal. Alternatively,conductors that extend in two or three of the directions can be formedin a single layer as long as they do not cross.

As illustrated in FIG. 8, a direction e₁ extends parallel to the "x"axis. A direction e₂ is rotated 60 degrees counterclockwise from thedirection e₁, whereas a direction e₃ is rotated 120 degreescounterclockwise from the direction e₁. If the directions e₁, e₂ and e₃are represented by vectors having a common length as illustrated in FIG.8, they form an equilateral triangle. For convenience, the notation e₁,e₂ and e₃ is used to denote the vectors that extend in the respectiverouting directions as well as the directions themselves. The radius ofthe circles that are inscribed by the hexagons 1300 is designated as ε.

The vectors e₁, e₂ and e₃ can be defined using the following notation.##EQU1##

A geometric structure in accordance with the present invention can alsobe defined using set theory. A set SIX(α, ε) of regular hexagons havecenters at points α, sides that are perpendicular to the vectors e₁, e₂and e₃₁, and radii of inscribed circles equal to ε as described above. Aset SU of points in a plane is denoted by x₁ e₁ +x₂ e₂, where x₁ and x₂are integers.

The set SIX(α, 1/2) for all α from the set SU intersect only on theedges of the hexagons and partition the plane into the closely packedarrangement that is illustrated in this example. Circles inscribed inthese hexagons are also densely packed.

As further illustrated in FIG. 8, the perpendicular distance "S" betweentwo adjacent conductors extending in the direction e₂, such asconductors 1304 and 1306, is equal to S=√3/2=0.87 measured in X-Ycoordinates, or S=√3ε=1.78ε. The perpendicular distances betweenadjacent conductors extending in the other two directions e₁ and e₂ isthe same as for the direction e₂.

An advantage of the present hexagonal routing arrangement is that thewirelength of conductors interconnecting two diagonally separatedterminals is typically substantially less than with conventionalrectilinear routing. As illustrated in FIG. 8, terminal points 1308 and1310 to be interconnected are located at (x,y) coordinates (0,0) and(3,√3), respectively.

Using the present routing arrangement, the points 1308 and 1310 can beconnected by a first conductor 1312 extending in the direction e₁ fromthe point 1310 to a point 1314 at coordinates (2,0), and a secondconductor 1316 extending from the point 1314 in the direction e₂ to thepoint 1310. The length of each of the conductors 1312 and 1314 is two,and the total connection length is four.

Using the conventional rectilinear routing method, connection betweenthe points 1308 and 1310 also requires the conductor 1312 from the point1308 to the point 1314. However, rather than the diagonal conductor1316, the conventional method requires two conductors, a conductor 1318from the point 1314 to a point 1320 at coordinates (3,0), and aconductor 1322 from the point 1320 to the point 1310.

The combined length of the conductors 1312 and 1318 is three, whereasthe length of the conductor 1322 is √3. The total length of theconventional rectilinear interconnect path is therefore 3+√3=4.73. Thepath length using a conventional rectilinear routing method between thepoints 1308 and 1310 is therefore 18.3% longer than the path lengthusing the tri-directional or hexagonal routing arrangement describedherein.

A reduction of 13% to 18% in pathlength is approximately an averagereduction that may be attained in many circuits using the presenthexagonal routing arrangement and three metal layers, althoughindividual cases can vary from this value. However, the distance betweenany two points using rectilinear routing typically will not be shorterthan that using the present hexagonal routing. On average, compared to aconventional rectilinear routing arrangement, the total length ofinterconnect wiring should be shorter using a hexagonal routingarrangement as described herein.

While the tri-directional routing (sometimes referred to as "hexagonalrouting") is described herein in connection with a hexagonal cell layouton a semiconductor substrate, such as the example illustrated in FIG. 8,the tri-directional routing may be advantageously used in connectionwith rectangular cells, as well as any other cell architecture. Thetri-directional routing invention disclosed herein is not limited tohexagonal cells. The advantages of the tri-directional routing describedherein are applicable to rectangular shaped cells, hexagonal shapedcells, triangular shaped cells, diamond shaped cells, square shapedcells, parallelogram shaped cells, trapezoidal shaped cells, any of theblocks shown in FIG. 91, polygonal shaped cells, irregular shaped cells,and any other type of cell. The tri-directional routing can be usedindependently of the particular underlying layout or architecture.

An example of a semiconductor device 30 that is interconnected using thehexagonal routing arrangement of FIG. 8 is illustrated in FIG. 9. Itwill be understood that the particular interconnect directions shown inthe drawing are selected arbitrarily for illustrative purposes, and arenot in any way limitative of the scope of the invention. In general, anyof the wiring directions can be utilized to interconnect any of theelements of the illustrated device 30.

In the illustrated example shown in FIG. 9, the terminals 1242, 1244,1246 and 1142 are interconnected internally. Conductors 1330, 1336 and1338 which extend in the e₁ direction are provided for connection of theterminals 1240, 1244 and 1140 respectively. Conductors 1332, 1334 and1340 which extend in the directions e₁, e₂ and e₃ are provided forconnection of the terminals 1158, 1156 and 1154 respectively. Theconductors 1332, 1334 and 1340, which carry input signals in thisexample, are preferably formed in different conductor layers.

FIG. 10 illustrates a microelectronic integrated circuit 1400 accordingto the present invention comprising a semiconductor substrate 1402 onwhich a plurality of devices 30 are formed in a closely packedtriangular arrangement. Further shown are a few illustrative examples ofinterconnection of the devices using the conductors 1330 to 1340 thatextend in the three directions e₁, e₂ and e₃.

It will be noted that six closely packed elements 1134 and 1234 define ahexagonal shape having a periphery 1350, and that twenty four closelypacked elements 1134 and 1234 define a larger hexagonal shape having aperiphery 1352. This relationship can be used within the scope of theinvention to provide unit cells having hexagonal shapes defined byclosely packed triangles, with internal structures similar to ordifferent from those which are explicitly described and illustrated.

It will be understood from the above description that the illustrateddevice geometry and three direction interconnect arrangementsubstantially reduce the total wirelength interconnect congestion of theintegrated circuit by providing three routing directions, rather thantwo. The routing directions include, relative to a first direction, twodiagonal directions that typically provide shorter interconnect pathsthan conventional rectilinear routing.

Reducing Intermetal Capacitance

FIG. 107 is a perspective view of a schematic illustration of aconventional rectilinear routing design. The wires or conductors 751 and752 in the first metal layer 750 shown in this example are parallel tothe wires or conductors 758 and 759 in the third metal layer 757. Thepotential for intermetal capacitance is increased by the parallelorientation of the metal wires. The illustrated wires 754, 755 and 756are in the second metal layer 753.

FIG. 108 shows a cross sectional view of the metal wires shown in FIG.107. Intermetal capacitance may occur between wires 759 and 752, asindicated generally by reference numeral 760. If the intermetalcapacitance results in a signal being induced in conductor 759 inresponse to a signal or pulse flowing through conductor 752 (or viceversa), this is referred to as crosstalk, and is highly undesirable inmost circuits. Intermetal capacitance may also occur between wire 755 inthe second metal layer 753, and wires 752 (in the first metal layer 750)and 759 (in the third metal layer), as indicated generally by referencenumerals 761 and 762. In addition, intermetal capacitance may occurbetween wires 755, 754 and 756 in the same metal layer 753, as indicatedgenerally by reference numerals 763 and 764.

Crosstalk occurs when a signal or pulse through conductor 755 induces asignal in an adjacent conductor 754 or 756. If the level of the inducedsignal in conductor 754 or 756 is relatively low, the induced signal maynot have an adverse effect upon the operation of the circuit. Typicalthreshold voltages have conventionally been about 0.8 volts, or even 0.5volts. If the induced signal level exceeds the threshold voltage of adevice connected to the conductor in which the signal is induced, it maycause the device to erronerously switch states or turn on. Dependingupon the device, the resultant consequences can be anything from aglitch to a devastating crash. The current trend is toward loweroperating voltages. Lower operating voltages have certain advantages,such as reduced power consumption and lower heat dissipation. As theoperating voltage is further reduced, the threshold voltages of thetransistors or other devices used in an implementation of the circuitwill typically be lower. Threshold voltages of 0.2 volts may becomecommon. Lower threshold voltages may exacerbate the adverse consequencesof crosstalk and induced voltages due to intermetal capacitance.

In some designs, the intermetal capacitance and crosstalk betweenconductors 755, 754 and 756 in the same metal layer 753 may be asignificant concern, especially where the wires 755, 754 and 756 runparallel to each other. Such an example is shown in the cross sectionalview of FIG. 109, wherein prime reference numerals represent likestructures having similar non-prime reference numerals. Intermetalcapacitance is typically greater when conductors are closer to eachother. Conductor 755' is much closer to adjacent conductors 754' and756' (see 764' and 763', respectively), than to conductors 759' and 752'(see 762' and 761', respectively). The relative distance 760' in thisexample between parallel conductors 752' and 759' in the first and thirdmetal layers 750' and 757', respectively, is relatively large ascompared to the distance 763' and 764' between adjacent parallelconductors 754', 755' and 756' in the same metal layer 753'. However, iftri-directional routing is used, two or three directions may be used inthe same metal layer to reduce the extent to which wires in the samemetal layer run parallel to each other. In some designs, this may onlybe necessary for some of the wires carrying certain signals, where otherconductors (carrying ground or V_(DD), for example) may be fabricatedhaving parallel wires without significant adverse consequences.

Using the tri-directional routing described herein, the number ofconductors that extend parallel to each other may be reduced as comparedto a conventional rectilinear routing design. In a three metal layerexample, the angles between conductors in different layers aresufficiently large (preferrably 60 degrees) that significant parasiticcapacitance between layers may be avoided, and parallel conductors indifferent metal layers may be avoided. The tri-directional routingdescribed herein reduces parasitic capacitance that is common inconventional rectilinear routing.

As will be described in detail below, the conductors that extend in thethree directions can be formed in three different layers, oralternatively the conductors that extend in two or three of thedirections can be formed in a single layer as long as they do not cross.Either alternative may be used to reduce intermetal capacitance.

The first alternative is illustrated in FIG. 110, which is a perspectiveview of a schematic illustration of a tri-directional routing example.In this example, wires 768 and 769 in the first metal layer 765 allextend in the same direction. Wires 770 and 771 in the second metallayer 766 all extend in the same direction, but it is a direction thatis angularly displaced relative to the direction of the wires 768 and769 in the first metal layer 765 by an angle of about 60 degrees. Wires772 and 773 in the third metal layer 767 all extend in the samedirection, but it is a direction that is angularly displaced relative tothe direction of the wires 768 and 769 in the first metal layer 765 byan angle of about 60 degrees, and it is a direction that is alsoangularly displaced relative to the direction of the wires 770 and 771in the second metal layer 766 by an angle of about 60 degrees. Thisalternative may be simpler to design, or suitable CAD tools for thisalternative may be easier to implement.

FIG. 28 illustrates an example of the second alternative where eachmetal conductor 407, 408 and 408 has certain portions of the conductorextending in each of three different directions, all in the same metallayer. In this example, the conductors 407, 408 and 409 representaddress lines in a memory array 400. The conductors 407, 408 and 409 donot cross each other at any point in the illustrated layout. Theillustrated memory array 400 is described in more detail elsewhere. Asimilar example is shown in FIG. 111.

Referring to FIG. 111, if it is necessary to make a connection between afirst wire 410 and a second wire 411 that must cross a third metalconductor 412 in the same metal layer 413, vias 414 and 416 may befabricated to establish electrical connection with a jumper conductor415 fabricated in another metal layer 417. In this example, a first via414 establishes an electrical connection between the first conductor 410and the jumper conductor 415. The first conductor 410 is fabricated inthe third metal layer 413. The jumper conductor 415 is fabricated in thesecond metal layer 417. A second via 416 is fabricated to establish anelectrical connection between the second conductor 411 and the jumperconductor 415.

In FIG. 4, the metal conductor 131 in the third metal layer 119 isangularly displaced from the metal conductor 128 in the second metallayer 118 by about 60 degrees, and is also angularly displaced from themetal conductor 122 in the first metal layer 117 by about 60 degrees. Inthis illustrated example, where metal conductors in each metal layer runin a single direction in that layer, no parallel wires will existbetween layers.

Parasitic and intermetal capacitance can be a problem in memory arrays.In a conventional two metal layer memory array, the bit lines and theselect lines are normally fabricated in the same layer of metal. Asmemory layouts are made smaller and smaller, the bit lines and theselect lines become closely packed. In addition to other adverseconsequences, this increases problems related to parasitic capacitanceand crosstalk, which may limit the performance and size of a memoryarray.

As explained more fully below, in the case of a DRAM cell, the linecapacitance can be a problem when it becomes large relative to thestorage capacitance of the cell storage devices. A DRAM array can onlytolerate a certain ratio of line capacitance to storage capacitance. Theonly way to favorably adjust the ratio of storage capacitance to linecapacitance in some conventional designs was to increase the storagecapacitance. The only practical way to increase the storage capacitancewas to increase the size of the cell. This had an adverse effect uponcell density, and became a limiting factor on how much a conventionalmemory array could shrink in size. In addition, the amount of storagecapacitance can become large enough to slow the speed of a memory array.

By routing select lines in a first metal layer, and bit lines in asecond metal layer, and power interconnect on a third metal layer,intermetal and line to line capacitance in a memory array is reduced. Inaddition, crosstalk is reduced.

The advantages of the tri-directional interconnect system may be appliedto reduce the intermetal capacitance in memory arrays, such as DRAMarrays, SRAM arrays, EPROM arrays, PROM arrays, ROM arrays, E² PROMarrays, and flash EPROM arrays. However, the tri-directional routingreduces intermetal capacitance in any circuit arraingement, and is notlimited to memory arrays.

Thus, a method of reducing intermetal capacitance in a microelectronicdevice may include the steps of fabricating a first layer ofinterconnect 765 having conductors extending in a first direction,fabricating a second layer of interconnect 766 having conductorsextending in a second direction that is non-orthogonally angularlydisplaced from the first direction, and fabricating a third layer ofinterconnect 767 having conductors extending in a third direction thatis non-orthogonally angularly displaced from the first direction, andthat is non-orthogonally angularly displaced from the second direction.The angular displacement between the first direction and the seconddirection is preferrably between about 50 degrees and about 70 degrees,and is more preferrably about 60 degrees. The angular displacementbetween the first direction and the third direction is preferrablybetween about 50 degrees and about 70 degrees, and is more preferrablyabout 60 degrees. The angular displacement between the second directionand the third direction is preferrably between about 50 degrees andabout 70 degrees, and is more preferrably about 60 degrees.

Hexagonal Cells

Transistors or cells in the shape of hexagons, triangles, and diamondstile well together, thus making efficient use of the surface spaceavailable on a semiconductor wafer and wasting as little real estate aspossible. This may be better understood with reference to FIG. 11.

FIG. 11 shows a plurality of closely packed hex shaped cells 160, 161,162, 163 and 164 laid out on the surface of a wafer. Hex shaped cell 163shares a common side with immediately adjacent hex shaped cell 160. Hexshaped cell 163 also shares a common side with immediately adjacent hexshaped cell 161. Similarly, hex shaped cell 163 shares a common sidewith immediately adjacent hex shaped cells 162 and 164, respectively.Cells in this shape tile well together so that no space on the surfaceof the wafer is wasted.

If desired, hex shaped cells 165, 166 and 167 may be laid out as shownin FIG. 12. For example, a channel 168 is formed between hex shaped cell166 and hex shaped cell 167. Similarly, a channel 169 is formed betweencells 166 and 165. And a channel 170 is formed between cells 167 and165. In some instances, a channel 169 or 168 may be desirable to allowroom for interconnect. In instances where such channels 168, 169 and 170are desired, the hex shaped cells 165, 166 and 167 will still tile welltogether with little or no wasted space.

Triangular shaped devices may tile well in the hexagonal architectureaccording to the present invention. FIG. 13 shows an example of a hexshaped cell 171. The hex shaped cell 171 is comprises six triangularshaped cells 172, 173, 174, 175, 176, 177 and 178. The cell 172 may be atriangular shaped device 172, or the cell 172 may be a group of devicesor gates laid out in the form of a triangle 172. It will be apparentthat triangular shaped cells 172, 173, 174, 175, 176, 177 and 178 whichare laid out as shown in FIG. 13 will tile together as shown in FIG. 11or FIG. 12. Any, or all, of the hex shaped cells 160, 161, 162, 163 and164 shown in FIG. 11 may be fashioned from six triangular shaped cells172, 173, 174, 175, 176, 177 and 178 as shown in FIG. 13. Similarly, thehex shaped cells 165, 166, and 167 shown in FIG. 12 may be formed bylaying out six triangular shaped cells 172, 173, 174, 175, 176, 177 and178 as shown in FIG. 13.

Programmable Devices Having Variable Gain Or Delay Characteristics

FIG. 14 illustrates a triangular shaped cell 179 that is particularlyadvantageous. The triangular shaped cell 179 may be configured in anumber of ways, as will be explained more fully below. In one example,the triangular shaped cell 179 may be configured as a transistor 179having a doped region 183 forming a source and a doped region 184forming a drain. Polysilicon 182 may be deposited as shown in FIG. 14over a suitable gate oxide (not shown). Of course, the gate oxide may begrown on the substrate in the illustrated region of the transistor 179,and a gate electrode 182 formed comprising suitably doped polysilicon.Manufacturing steps for fabricating such structure is known to thoseskilled in the art. A first contact 180 may be formed for the source tofacilitate interconnection of the transistor 179 to other devices.Similarly, a second contact 181 may be formed to permit interconnectionof the drain 184 of the transistor 179.

The gate 182 may be located in a different position relative to thesource 183 and drain 184 to fabricate a transistor 179 providing ahigher or lower drive current. This is a programmable design in that atransistor having a range of desired drive currents may be fabricatedfrom this triangular transistor 179 design by changing the location ofthe gate 182.

The programmability of this design may be better appreciated bycomparing the transistor 187 shown in FIG. 15. The transistor 187 has asource 188 and a drain 189. A first contact 190 for the source andsecond contact 191 for the drain are provided. In the exampleillustrated in FIG. 15, a gate 192 is formed by the polysilicon 192. Thechannel width 193 of the gate 192 is smaller than the channel width 194shown in FIG. 14. The smaller channel width 193 of the transistor 187shown in FIG. 15 will result in a lower drive current for a givenvoltage on the gate 192 as compared with the transistor 179 shown inFIG. 14.

The transistor 197 shown in FIG. 16 has a source 198 and a drain 199. Afirst contact 200 for the source and second contact 201 for the drainmay be provided for interconnection. In the example illustrated in FIG.16, a gate 202 is formed by the polysilicon 202. The channel width 203of the gate 202 is larger than the channel width 194 shown in FIG. 14.The larger channel width 203 of the transistor 197 shown in FIG. 16 willresult in a higher drive current for a given voltage on the gate 202 ascompared with the transistor 179 shown in FIG. 14. If the depth of thechannel is the same, then the drive current for a transistor 197 with achannel width 203 three times the size of a second transistor 187 shouldbe three times greater.

Alternatively, the delay of devices may be similarly programmed. For agiven fixed current, a transistor 197 with a larger channel width 203 asshown in FIG. 16 will have a longer delay than a transistor 187 with asmaller channel width 193 as shown in FIG. 15.

The gate electrode 192 shown in FIG. 15 has a width 216. If the width216 is made larger, the transistor 187 will be slower. If the width 216is made smaller, the transistor 187 will be faster. Thus, the speed ofthe transistors 187 may be programmed during the final fabrication stepsto provide any desired speed within a possible range which may be neededin a circuit by adjusting the width 216 of the gate electrode 192.

In addition, the thickness of the gate can be changed to reduce (orincrease) the current. This is illustrated in FIGS. 20C and 20D. Thethicker gate electrode 266 as compared to the gate electrode 267 shownin FIG. 20C results in less current through the respective transistors.

The triangular transistor 179 described herein provides a programmabledesign that permits partial prefabrication of a substrate having thestructure shown in FIG. 14 except that no gates 182 (or source/drainregions) are formed. The wells and isolation structures of thetransistors are made in advance, to thereby make inchoate transistorstructures. This may provide an especially quick method for implementingcustom circuit designs in silicon using such partially prefabricatedsubstrates. A substrate having such partially fabricated inchoatetransistors 179 may be made in advance, and then used to build anydesired circuit by laying down gates 182, forming source/drain regions,and interconnecting the transistors 179. The gates 182 may be laid downas shown in FIG. 14, FIG. 15, or FIG. 16, depending on the size of thetransistors that are needed to construct the desired circuit. Forexample, if a large transistor is needed at a given point in thecircuit, a "large" transistor like the transistor 197 shown in FIG. 16may be fabricated by placing the gate electrode as shown. Different sizetransistors may be needed at different points in the desired circuit,and it will be appreciated that some transistors may be constructed asshown in FIG. 14, some as shown in FIG. 15, and some as shown in FIG.16. An advantage of this arrangement is that all transistor structuresare the same size. "Larger" transistors actually occupy the same amountof real estate; the transistors are fabricated as "large" transistorssimply by locating the gate electrode in the appropriate locationrelative to the triangular structure. Of course, the arrangements shownin FIG. 14, FIG. 15 and FIG. 16 are not the only possible examples.These embodiments are illustrative only, and variations in theillustrated examples are also possible.

Referring to FIG. 14, two transistors 179 may be simultaneouslyfabricated from the illustrated arrangement. A second drain 185 isprovided having a common source 183. The second drain 185 is providedwith a third contact 186 for interconnection. The second transistor 179has a common gate 182.

Similarly, the transistor 187 shown in FIG. 15 may have a secondtransistor having a common source 188, common gate 192, and a drain 196with a third contact 195. The transistor 197 shown in FIG. 16 may alsohave a second transistor having a common source 198, common gate 202,and a drain 204 with a third contact 205.

It will be understood that the terms "source" and "drain" as applied tofield effect transistors merely define opposite ends of a channel regionwhich is controlled by a voltage applied to a gate. The source and drainare interchangeable in that current may flow into either one and out ofthe other. Therefore, the terms "source" and "drain", and the relativepolarities of voltages applied thereto, which may be described in theexamples illustrated in the present specification, are arbitrary andreversible within the scope of the invention, and are not to beconsidered as limiting the invention to one or the other of the possibleconfigurations of polarities.

Field Programmable Gate Array

FIG. 125 shows a schematic diagram of a field programmable devicesuitable for use in a gate array or the like. A transistor 815 may havethe equivalent of a "fuse" 816, so that if the fuse 816 is broken (byprogramming the array devices in the field) the transistor 815 isrendered inoperative. FIG. 126 shows a layout of a field programmabledevice 817. The programmable fuse is represented by the terminal 818.The device 817 shown in FIG. 126 has three potential transistors with acommon source/drain 819. Gate electrodes 822, 823 and 824 are formed bypolysilicon layers. A source/drain terminal 821 and a source/drainterminal 820 are also shown.

FIG. 127 shows an example of a hexagonal cell 825 comprising six of thestructures shown in FIG. 126 arrainged in an array. The devices areprogrammed by selecting either column line 828, or column line 829, orcolumn line 830. This action potentially selects two programmabledevices in each column. The device to be programmed is finally selectedby turning on either common gate 826, or common gate 827. Because eachcommon gate 826 or 827 only potentially selects only one programmabledevice in each column, a device to be programmed may be uniquelyselected by selecting the desired column 828, 829, or 830, and byselecting the desired row 826 or 827.

FIG. 128 illustrates a cross-sectional view of one embodiment of a fieldprogrammable E² PROM 831. A gate 832 is provided, and a floating gate833 is included to permit the device 831 to be programmed. Source 834and drain 835 connections are shown schematically. Of course, fieldoxide regions 836 are form in a manner known in the art. By using a highprogramming voltage, a selected device can be programmed by injectingcharge from the substrate 837, causing charges to tunnel through to andbuild up on the floating gate 833 in a manner known in the art. A device831 may be deprogrammed by sucking the charge from the floating gate 833in a manner known in the art.

Hexagonal Cells Comprising Triangular Devices

Referring to FIG. 17, triangular cells 206 such as the transistors 179shown in FIG. 14 may be fabricated on a semiconductor substrate asshown. The triangular devices 206 may be arranged as hexagons (see FIG.13) and tile together well as shown in FIG. 17.

Triangular devices 206 tile together well in a diamond shapedconfiguration as shown in FIG. 18. Triangular devices 206 tile togetherwell in a larger triangle shape or megafunction 207 shown in FIG. 19.Six of the megafunctions 207 may be tiled together as shown in FIG. 13to form a large hexagonal shaped megafunction. These illustratedgroupings show various expansion cells or functions made up of smallerhexagonal or triangular functional blocks. In the architecture accordingto the present invention, diamond shaped cells as shown in FIG. 18 maytile well with hexagonal shaped cells as shown in FIG. 13 or FIG. 17,and with triangle shaped cells 207 as shown in FIG. 19. The hexagonalarchitecture according to the present invention may provide the mostcompact way to partition the available area on a semiconductorsubstrate.

Although the cells shown in FIG. 17, FIG. 18 and FIG. 19 are shown asclosely packed, the cells may alternatively be laid out with channelsproviding space for routing interconnections, such as the channels 168,169, 170 shown in FIG. 12.

Tri-ister Structure

An alternative embodiment of a triangular structure 208, which may bereferred to as a tri-ister, is depicted in FIG. 20. In this example,three transistors may be formed in a single triangular shaped cell 208.A common gate electrode 215 divides the structure 208 into a dopedregion 209 having a contact 210 that may be a source. A doped region 211having an electrode contact 212 may be a drain. A doped region 213having an electrode contact 214 may be a second drain. A firsttransistor may have a source 209 and drain 213. A second transistor mayhave a source 209 and drain 211. The region 213 may function as a sourcerelative to region 211, forming a third transistor having a source 213and drain 211.

An example of a layout of a tri-ister 670 is shown in FIG. 112. A dopedregion 671 may be a P-well or an N-well, depending upon whether thetri-ister 670 is a PMOS or NMOS device. A first source/drain terminal673 provides electrical connection to interconnect 680, which in thiscase is connected to a voltage V_(DS1). A second source/drain terminal674 provides electrical connection to interconnect 681, which isconnected to a voltage V_(SS). And a third source/drain terminal 672provides electrical connection to interconnect 679, which in this caseis connected to a voltage V_(DS2). The terminals 672, 673 and 674 maycomprise vias to electrically connect the doped region 671 with a metallayer.

Polysilicon 675 is used to form a first gate electrode 677, a secondgate electrode 678, and a third gate electrode 676. The gate electrodes676, 677, and 678 comprise a common gate electrode in the illustratedexample. A first or main transistor 688 is formed by the source 673,drain 674, and gate 677. A second transistor 687 is formed by the source672, drain 674, and gate 678. A third transistor 689 is formed by thesource/drain terminal 672, the source/drain terminal 673, and the gate676.

A terminal or via 684 provides electrical connection to interconnect 682in order to facilitate connection of other circuit components to thegate electrode 677. A terminal or via 685 provides electrical connectionto interconnect 683 in order to facilitate electrical connection ofother circuit components to the gate electrode 678. A P-well 686 is alsoshown in this particular example. The P-well 686 is preferrablyconnected to the voltage V_(SS).

An example of an NMOS tri-ister structure 670 may be constructed inaccordance with one aspect of the present invention as illustrated inFIG. 112. Voltage curves, current curves, and transistor characteristicsmay be determined for the main transistor 688 formed by the source 673,drain 674, and gate 677. Measurements were made from the first terminal673, which was at the voltage V_(DS1), to the second terminal 674, whichwas at the voltage V_(SS). The voltage V_(DS2) applied between the thirdterminal 672 and the second terminal 674 was used as the controllervoltage. The main transistor 688 voltage-current curves controlled byvoltage V_(DS2) are shown in FIG. 113. Table 1 shows the range of thevariables which were used to generate the curves shown in FIG. 113. Thestart value, stop value, and step size for each variable voltage isgiven in volts. The values of the constant voltages are set forth involts. In Table 1, "VG1" is the gate voltage, "VDS2" is the voltageV_(DS2), "VDS1" is the voltage V_(DS1), and "VB" is the voltage V_(SS).Both the subthreshold slope and the threshold voltage V_(T) arebasically independent of the voltage V_(DS2).

However, the drive current is dependent upon the voltage V_(DS2). Inaddition, the effective channel width of the main transistor 688 can becontrolled by the voltage V_(DS2). That is, by varying the voltageV_(DS2), the main transistor 688 can be controlled to behave as if it iseither (a) a transistor that has a certain channel width W, or (b) atransistor that has a certain channel width 2W that is twice as wide,even though the physical dimensions of the transistor 688 are notactually changed. This is referred to as changing the "effective channelwidth." In this example, the effective channel width of the maintransistor may be electronically switched from W to 2W by changing thevoltage V_(DS2). Thus, in a tri-ister structure 670 according to oneaspect of the present invention, the effective channel width of a firsttransistor 688 formed by a first source/drain terminal 673, gate 677,and a second source/drain terminal 674 may be dynamically switched todouble it (or conversely half it) using a control voltage V_(DS2)between a third source/drain terminal 672 and the second source/drainterminal 674. The tri-ister 670 comprises a transistor 688 havingdynamically adjustable transistor characteristics. The drive current ofthe first transistor 688 is dependent upon, and thus may be changed by,the voltage V_(DS2).

FIG. 114 shows the main transistor 688 drain-to-source current vs. thesource-drain voltage, controlled by the voltage V_(DS2). In thisexample, the gate voltage applied to the gate electrode 677 was about3.3 volts. These curves show the effective channel width switching whichis possible in accordance with one aspect of the present invention. Forexample, when the voltage V_(DS2) =3.3 volts and the voltage V_(DS1) =0volts, the drain-to-source current for the main transistor 688 is 1.4mA. This current is doubled when the voltage V_(DS2) =0 volts and thevoltage V_(DS1) =3.3 volts, i.e., the drain-to-source current for themain transistor 688 is 2.8 mA. Those skilled in the art will appreciatethat this indicates that the effective channel width is switchingbetween W and 2W in this example.

Table 2 shows the range of the variables which were used to generate thecurves shown in FIG. 114. The start value, stop value, and step size foreach variable voltage is given in volts. The values of the constantvoltages are set forth in volts. In Table 2, "VG1" is the gate voltage,"VDS2" is the voltage V_(DS2), "VDS1" is the voltage V_(DS1), and "VB"is the voltage V_(SS).

The transistor characteristics of an example of a PMOS tri-ister 670 areset forth in FIGS. 115, 116, 117, 118 and 119, and the accompanyingTables 3, 4, 5, 6 and 7, respectively. The Tables accompanying eachFigure show the range of the variable voltages, and the constant valuesassociated with the curves depicted in each such Figure.

FIG. 115 shows the main transistor 688 drain current verses thedrain-to-source voltage, controlled by the gate voltage at V_(DS2) =0volts, normal. The accompanying Table 3 shows the range of the variablevoltages, and the constant values associated with the curves depicted inFIG. 115.

FIG. 116, Table 4, and Table 9 show the main transistor 688 subthresholdat V_(DS2) =0 volts, normal, 87 mV/dec, and a threshold voltage V_(T) ofapproximately -1 volt. FIG. 117, Table 5, and Table 10 show the maintransistor 688 current-voltage curves controlled by V_(DS2). Both thesubthreshold slope and the threshold voltage V_(T) are essentiallyindependent of the voltage V_(DS2). However, as discussed above, in thisexample the current drive is dependent upon the value of the voltageV_(DS2). Thus, the effective channel width may be switched between 2Wand W by changing the voltage V_(DS2). FIG. 118 and Table 6 show themain transistor 688 drain-to-source current verses the drain-to-sourcevoltage at a gate voltage of -3.3 volts, controlled by V_(DS2). WhenV_(DS2) =-3.3 volts, and V_(DS1) =0 volts, the drain-to-source currentis 0.7 mA, which is half of the drain-to-source current (1.4 mA) whenV_(DS2) =0 volts and V_(DS1) =-3.3 volts. This indicates that theeffective channel width is switching from W to 2W responsive to a changein the voltage V_(DS2). FIG. 119 and Table 7 show the main transistor688 drain-to-source current verses the voltage V_(DS1) at V_(DS2) =-3.3volts, showing distorted current-voltage curves.

FIG. 120 shows a layout for two tri-isters 690 and 691 configured as aninverter circuit, which is indicated generally by reference numeral 699.The inverter 699 has an input 692, which in the illustrated example isprovided by interconnect 776. The voltage at input 692 is referred to asV_(IN). The inverter 699 has an output 693, which is provided bysuitable interconnect. The voltage at output 693 is referred to asV_(OUT). A V_(DD) voltage (sometimes referred to as V_(S2)) is appliedto interconnect 694. A V_(SS) voltage (sometimes referred to as V_(S1))is applied to interconnect 695. A voltage referred to as V_(D1) isapplied to interconnect 696. A voltage referred to as V_(D2) is appliedto interconnect 697. In the illustrated example, the voltage V_(DD) isalso applied to an N-well 668, and the V_(SS) voltage is applied to aP-well 669.

The structure of the tri-isters 690 and 691 is similar to the tri-isterillustrated in FIG. 112. The tri-ister 690 has a Y-shaped common gatestructure 775, which is electrically connected to the input 692 througha terminal or via 778. The tri-ister 691 also has a Y-shaped common gate780. The two Y-shaped gates 775 and 780 are electrically connected toeach other by interconnect 779 through terminals or vias 781 and 782.

A source/drain terminal 783 of the tri-ister 690 is connected to V_(D1)by interconnect 696. The source/drain terminal 784 of the tri-ister 690is connected to V_(DD) by interconnect 776. The source/drain terminal786 of the tri-ister 691 is connected to V_(SS) by interconnect 777. Thesource/drain terminal 787 of the tri-ister 691 is connected to V_(D2) byinterconnect 697. The source/drain terminal 785 of the tri-ister 690 isconnected to the source/drain terminal 788 of the tri-ister 691 byinterconnect 789, which is also electrically connected to the output 693and the voltage V_(OUT).

The operation of the inverter circuit 699 may be understood by thoseskilled in the art from the information depicted in the graphs of FIGS.121, 122 and 123, and the associated Tables 11, 12 and 13, respectively,in which V_(D1) and V_(D2) are used as controllers. FIG. 121 shows aninverter transfer curve when V_(D1) and V_(D2) are floating, normal,maximum noise margin, and zero standby dissipation. Table 11 shows thestart and stop values, and step size, for the variable V_(IN). I_(OUT)referred to in Table 11 is the current flowing out of the output 693.FIG. 122 shows an inverter transfer curve controlled by V_(D2) whenV_(D1) =3.3 volts, abnormal. Table 12 shows the start and stop values,and step size, for the variables V_(IN) and V_(D2). FIG. 123 shows aninverter transfer curve controlled by V_(D1) when V_(D2) =3.3 volts,normal, decreasing noise margin, non-zero standby power dissipation.Table 13 shows the start and stop values, and step size, for thevariables V_(IN) and V_(D1).

A tri-ister 670, such as the example shown in FIG. 112, has a commongate electrode 675 for the three potential transistors 688, 687 and 689.The common gate electrode 675 is generally fabricated in the shape ofthe letter "Y." Thus, the Y-shaped gate is a characteristic of apreferred embodiment of a tri-ister. Consequently, a tri-ister may alsobe referred to as a Y-gate structure or device. The three devices ortransistors 688, 687 and 689 may be referred to as potential transistorsbecause it is not necessary for all three devices to be used astransistors, or used at all.

Referring to FIG. 20, if the tri-ister device 208 is biasedappropriately, a first current i₁ can flow from the source region 209 tothe drain region 213. Under a given biasing condition, it is possible tomodulate the first current i₁ and affect a second current i₂ flowingfrom the source region 209 to the drain region 211. Under certainbiasing conditions, the current i₃ flowing from region 213 to region 211may be adjusted to be equal to the current i₁ flowing from region 209 toregion 213. In this particular example, the net current flowing out ofelectrode 214 would be zero. This may have advantageous applicationswhich will be apparent to those skilled in the art.

FIG. 20A illustrates a configuration where the terminal 214 is connectedto a resistor 264, which in turn is connected to a constant currentsource 265. The current i₃ flowing from terminal 214 to terminal 212will be equal to the current i₁ minus the constant current i₄. Themagnitude of the current i₃ will be a function of the magnitude of thecurrent i₁, and the direction of flow of the current i₃ will depend onwhether the magnitude of the current i₁ is greater than the value of i₄.Therefore, the current i₁ may be used to modulate the current i₃.

Referring to FIG. 20B, in this configuration, the current i₁ flowingfrom terminal 210 to terminal 214 in the tri-ister structure 208 cannotbe equal to the current i₃ flowing from terminal 214 to terminal 212,because the current i₄ flowing from terminal 214 to ground would have tobe zero in that case. A resistor R indicated by reference numeral 263 isconnected between terminal 214 and ground. If no current flowed throughthe resistor 263, the voltage drop across the resistor 263 will be zero,and the terminal 214 would tend to float to a voltage approachingV_(DD). Under those circumstances, a current i₄ equal to the voltagedrop across the resistor 263 times the resistance would begin to flow,and the current i₄ could not be zero under those conditions. The currenti₃ flowing from terminal 214 to terminal 212 would therefore have to beless than the current i₁ flowing from terminal 210 to terminal 214.

FIG. 20C depicts an example of a tri-ister 208' in which the gate 266for the transistor formed between the terminal 210' and the terminal214' has a wider channel width. This will reduce the current i₁ flowingfrom terminal 210' to terminal 214' all other things being equal. Thetransistor formed between the terminal 210' and the terminal 212' has arelatively narrow channel 267, thus providing a higher current i₂ allother things being equal. In this example, the tri-ister structure 208'may be configuraed where the current i₂ is a multiple of the current i₁for any given gate voltage.

FIG. 20D shows a configuration for a tri-ister structure 208" which issimilar to that depicted in FIG. 20C. The terminal 212" is connected toa resistor 269, which is in turn connected to ground. The voltage dropacross the resistor 269 will be a function of the net current flowingout of the terminal 212". The relative gate dimensions may be fabricatedto achieve certain desired operating characteristics and relativecurrent values.

The tri-ister structure 208 may be used in a configuration as anoperational amplifier. The tri-ister structure 208 may also beconfigured as a triode transistor.

FIG. 124C shows an operational amplifier or op amp 790. The op amp 790has a first input 791, a second input 792, and an output 793. FIG. 124Ashows one example of a partial layout for an op amp 790. FIG. 124B showsa schematic diagram of an equivalent circuit for the structure depictedin FIG. 124A.

Referring to FIG. 124A, a layout for a triangular structure forming PMOStransistors 804 and 805 is shown interconnected with a triangularstructure forming NMOS transistors 803 and 806. The source 800 for thetransistor 803 is connected by interconnect 801 to a polysilicon layer794 forming a common gate for two transistors 803 and 806. Thetransistor 806 has a common drain with transistor 803, and both areconnected to ground by interconnect 796. A polysilicon layer 808 formingthe gate electrode for transistor 804 is connected to the second input792. Similarly, a polysilicon layer 809 forming the gate electrode fortransistor 805 is connected to the first input 791. The transistor 804has a common source with the transistor 805, and both are connected byinterconnect 795 to a current source 799. The source of the transistor806 is connected to the drain of the transistor 805 by interconnect 797,and both are connected to the gate of a transistor 807. The drain of thetransistor 807 is grounded, and the source is connected to a secondcurrent source 798. If desired, a COMP connection may be made at thepoint indicated by reference numeral 810 in FIGS. 124A and 124B.

Referring to FIG. 20, the tri-ister 208 can operate as a tri-statedevice. For example, the terminal 212 and the terminal 214 can both beconfigured as drains. The current will be shared between the transistorformed with source 210/drain 214 and the transistor formed with source210/drain 212. When one of these two transistors is turned off, or thedrain changed to a source, it will double the current to the othertransistor. It is possible to change the direction of the current bychanging the voltage. Instead of doubling the current, of course, theconverse operation could be used to half the current. The three stateswill then be (1) off, (2) on with current I, and (3) on with current 2I.

Another embodiment of a useful device 841 is shown in FIG. 130. Thisstructure provides four potential transistors, and may be referred to asa quad-ister. A common gate electrode 847 is shown. Source/drainterminals 843, 844, 845 and 846 are also shown.

Memory Cells

A hexagonal architecture may be advantageously applied to the design ofa memory circuit, such as an SRAM circuit or a DRAM circuit.

For example, FIG. 21 is a top view of an SRAM cell 219. Using ionimplantation steps known in the art, an NMOS island or n type diffusionregion 220 may be formed in the semiconductor substrate. A PMOS islandor p type diffusion region 221 may be formed using ion implantation ordoping in a manner known to those skilled in the art. Similarly, an NMOSregion 228 and a PMOS region 229 may be formed. Local interconnect 226may be laid down as shown. Local interconnect 234 is also provided.Polysilicon layers 225, 230, 235 and 236 may be insulated from structureimmediately below the polysilicon layers by an intervening layer ofoxide (not shown). A metal interconnect 227 provides electricalconnection between the polysilicon layer 225 and the local interconnect234. The local interconnect 234 is electrically connected to the NMOSregion 228. The metal interconnect 227 is electrically insulated fromthe local interconnect 226 and the polysilicon layer 230. Localinterconnect 226 provides electrical connection between the NMOS island220 and the polysilicon layer 230. Metal contacts 223, 222, 224, 233,231 and 232 are provided to facilitate electrical connections.

In the example illustrated in FIG. 21, the NMOS region 228 forms asource 237 and a drain 238, with the polysilicon 230 operating as a gateelectrode. Similarly, source and drain regions are formed on oppositesides of the polysilicon gate electrodes 225, 235, 236 and 230 wherethey cross NMOS regions 220 and 228 and PMOS regions 221 and 229. Localinterconnect 239 provides electrical connection between the NMOS region220 and PMOS region 221. Local interconnect 240 provides electricalconnection between the NMOS region or island 228 and the PMOS region orisland 229.

The metal contacts 224 and 233 provide ground connections. V_(DD)voltage is applied to metal contacts 223 and 232. The bit line isconnected to the metal contact 222. The metal contact 231 provideselectrical connection to the complement of the bit line, sometimesreferred to as the "bit bar" line. The polysilicon 235 is electricallyconnected to the polysilicon 236 (the connection has been omitted forclarity), and both are connected to an address line. This illustratedSRAM cell may provide an advantageous layout for a memory circuit.

An alternative embodiment of the cell layout 219 shown in FIG. 21 mayflip the orientation of the lower half of the cell so that the groundconnections 224 and 233 are on opposite sides. This may allow for moreconvenient connections between the top half of the cell 219 and thebottom half.

FIG. 22 shows a top view of another possible layout for a memory circuit241. The illustrated example may provide a layout having a cell sizethat is one-half to one-third the size of a conventional prior artlayout for the same circuit. The memory circuit 241 illustrated in FIG.22 comprises a plurality of triangular structures 242. Two triangularstructures 241 comprise a diamond shaped cell.

The triangular structures 241 have polysilicon 252, 253 and 254 whichform gate electrodes. The gate electrodes 252 will be connected invarious ways which are not shown for clarity. The triangular structures241 also have electrodes 255, 256 and 257 to facilitate electricalconnections to source regions.

Most of the triangle structures 242 shown comprise a small PMOStransistor 245 which controls the current. The triangle structures 242have a larger NMOS transistor 244. The triangle structures 241 also havea third transistor 243 used for addressing. The third transistor 243 isconnected to a bit line 249. These three transistors 243, 244 and 245have a common drain region 246. A ground connection 247 provides acommon ground for surrounding triangular structures 242. Metalinterconect connects the data outputs to form a bit line 249. A metalbit bar line 250 provides the logical complement of the bit line. Asecond bit line 251 is also shown. Although these lines are metal inthis example, they need not be; polysilicon could be used for example.

In a preferred embodiment of the circuit shown in FIG. 22, three layermetal routing employing hexagonal architecture is used. The metal bitlines 249 and 251 are shown extending in a first metal layer that is ina direction that is horizontal in FIG. 22. Address lines 258 arefabricated in a second metal layer providing connections in a directionthat is angularly displaced sixty degrees from the direction of the bitlines 249 and 251. Power line connections 259 are provided in a thirdmetal layer that is angularly displaced sixty degrees from the directionof the bit lines 249 and 251. The direction of the power lineconnections 259 are also angularly displaced sixty degrees from thedirection of the address lines 258.

FIG. 22A is a schematic diagram of an equivalent circuit 270 to thatimplemented with the structure shown in FIG. 22. The NMOS transistor 244shown in FIG. 22 is shown schematically as transistor 271 in FIG. 22A.The small PMOS transistor 245 shown in FIG. 22 is shown schematically astransistor 272 in FIG. 22A. The transistor 243 shown in FIG. 22 which isused for addressing is shown schematically as transistor 273 in FIG.22A.

The bit line 249 in FIG. 22 is shown schematically as the bit line 274in FIG. 22A. The address line 258 in FIG. 22 is shown schematically asthe address line 275 in FIG. 22A. The power line 259 in FIG. 22 is shownschematically as the V_(DD) or power line 276 in FIG. 22A. Theconnection to ground or V_(SS) is shown in FIG. 22A by the referencenumeral 277, which corresponds to the ground connection 247 in FIG. 22.As described with reference to FIG. 22, a cell 270 is made up of twotriangular structures 242. The second triangular structure 242 will havethree corresponding transistors, which are shown schematically in FIG.22A as transistors 279, 278 and 280.

Sense Amplifier

FIG. 23 is a top view of the layout of a triangular structure 630implementing a sense amplifier circuit suitable for use in connectionwith an SRAM, although the circuit is not necessarily limited to SRAMs.The sense amplifier circuit will operate satisfactorily in connectionwith the DRAM cell shown in FIGS. 23B and 23C. The sense amplifiercircuit includes a first transistor 631, a second transistor 632, and athird transistor 633. The source region 634 of the first transistor 631is connected to V_(SS) or ground 636, which is shown schematically inFIG. 23. The first transistor 631 has a first gate electrode 637, whichis connected to V_(G3). The first, second and third transistors 631, 632and 633 have a common source/drain region 635. A second gate electrode638 for the second transistor 632 is connected to V₁. A third gateelectrode 639 for the third transistor 633 is connected to V₂.

The drain 640 of the second transistor 632 is connected to a polysiliconlayer 641 which functions as an electrical contact. A first resistor 642may be formed by providing a region indicated by reference numeral 642that is not doped. Alternatively the resistor region 642 may be lightlydoped as desired to adjust the amount of resistance to a desired value.In this example, the polysilicon layer continues with a doped region 643that is electrically connected to V_(DD). The resistor 642 mayalternatively be formed using a channel region of an FET. Other methodsand structures known to those skilled in the art may be utilized toprovide the functional equivalent of a resistor 642.

FIG. 23 shows a drain 644 of the third transistor 633 electricallyconnected to a doped polysilicon layer 645 to provide an electricalconnection to a second resistor 646. In the illustrated example, thesecond resistor 646 comprises a region that is not doped, or is lightlydoped, as described above with reference to the first resistor 642. Thepolysilicon layer continues with a doped region 647 that is electricallyconnected to V_(DD). As described above, the resistor 646 may be formedusing a channel region of an FET, by stretching the island 635, or anyother alternative structure known to those skilled in the art forconstructing resistors on a semiconductor substrate.

In this example, the contacts 641, 643, 645 and 647 comprisepolysilicon. However, the polysilicon layer 641, and the polysiliconlayer 643, may be constructed as a metal routing layer. Similarly, theelectrical connections established by the polysilicon layers 645 and 647may be accomplished with metal routing. In this alternative example,over-the-cell routing may be used to route electrical connection 645,646, and 647 over the gate electrode 639, and to route the electricalconnection 641, 642 and 643 over the gate electrode 638. Theinterconnect 647 and the interconnect 643 may be fabricated as a unitarystructure to provide a common V_(DD) connection. The resistors 642 and646 may be constructed using an alternative approach from thepolysilicon described with reference to the illustrated embodiment shownin FIG. 23. The value of the resistors may affect the magnitude oramplification of the sensed voltage. Typically, the amplification factoris multiplied times the difference in the sensed voltages V₁ and V₂ todetermine the output.

FIG. 23A depicts a schematic diagram of a sense amplifier circuit 650that corresponds with the sense amplifier circuit 630 implemented withthe structure shown in FIG. 23. Referring to FIG. 23A, the senseamplifier circuit 650 includes a first transistor 651, a secondtransistor 652, and a third transistor 653. Each transistor 651, 652,and 653 has a source, a gate, and a drain, although the source and drainmay be interchanged arbitrarily. The source 654 of the first transistor651 is connected to V_(SS) or ground. The first transistor 651 has afirst gate 657 which is connected to V_(G3). The first, second and thirdtransistors 651, 652 and 653 have a common source/drain connection 655.The gate 656 for the second transistor 652 is connected to V₁. The gate658 for the third transistor 653 is connected to V₂.

A first resistor 659 is connected between the drain 661 of the secondtransistor 652 and a V_(DD) line 663. A second resistor 660 is connectedbetween the drain 662 of the third transistor 653 and the V_(DD) line663.

The bit line of a column of a memory array that is to be read is coupledor switched to either terminal 656 (V₁) or to terminal 658 (V₂). Thecircuit is symetrical, so it will operate equally well regardless ofwhich terminal 656 or 658 is used. The other terminal 656 or 658 isconnected to a reference voltage. The sense amplifier 650 is turned onby driving voltage V_(G3) on terminal 657 high. This causes transistor651 to turn on, and energizes the sense amplifier 650. The transistor651 may be used to turn the amplifier off to conserve power when memoryis not being read.

If the terminal 656 is connected to the column being read, the voltageV₁ will cause the transistor 652 to conduct if the cell being read ishigh. When the transistor 652 conducts, current flows from V_(DD)through resistor 659 and through transistor 652. The current will causea voltage drop to occur across resistor 659. This will drive the outputvoltage on output terminal 664 low. The difference in the voltagesacross output terminal 664 and output terminal 665 can be read todetermine the logical state of the bit stored in the cell being read.The remaining details of operation of the sense amplifier 650 shown inFIG. 23A should be apparent to those skilled in the art, after havingthe benefit of the description set forth herein.

A DRAM Cell

FIG. 23B shows a triangular DRAM cell 281 constructed in accordance withone aspect of the present invention. This triangular DRAM cell 281 hasseparate read select line 290 and write select line 288. The illustratedtriangular DRAM cell 281 has a separate read bit line 289 and write bitline 287. The provision of separate read and write input and outputs 289and 287 greatly facilitates the implementation of separate read/writeports for a memory array constructed using the illustrated DRAM cell281. This circuit element 281 can be easily configured for multiportmemories.

FIG. 23C shows the storage element 284, which is implemented withcapacitance shown in the equivalent circuit as a capacitor storagedevice 283, and an associated first transistor 282. The layout depictedin FIG. 23B advantageously uses the gate capacitance of the transistor282 to provide the necessary storage capacitance 283. In the layout ofFIG. 23B, a layer of doped polysilicon forming a Y-shaped capacitorplate gate electrode, with a triangular capacitor plate electrode 261inversely oriented with respect to the triangular cell 281. Thepolysilicon 261 serves a dual function as the gate electrode for thefirst transistor 282 and one plate of the capacitor 283. The dopedpolisilicon gate is speced from and insulated by the gate dielectric,which provides the dielectric for the capacitor 283.

The gate of the first transistor 282 is connected to the drain 260 of asecond transistor 285. In the layout shown in FIG. 23B, this isaccomplished using a shorting strap 293. The illustrated embodiment isshown with a short silicide strap 293 that may be fabricated as localinterconnect. The drain of the second transistor 285 is connected to thewrite bit line 287. The gate of the second transistor 285 is connectedto the write select line 288. When the signal on the write select line288 goes high, it turns on the second transistor 285 and drives node 260high. The signal on the write line 287 will be coupled to the storagecell 284, and will drive the first transistor 282 into conduction if thewrite signal is high, and will not turn on the first transistor 282 ifthe write signal 287 is low.

The source of a third transistor 286 is connected to the drain of thefirst transistor 282. In other words, the first and third transistors282, 286 have a common source/drain connection 291. The gate of thethird transistor 286 is connected to the read select line 290. The drainof the third transistor 286 is connected to the read bit line 289. Whenthe read select line 290 goes high, the third transistor 286 will bedriven to conduct, and will couple the read bit line to the storage cell284. The presence or absence of a charge stored in the capacitor 283 ofthe storage cell 284 can be sensed. The sense amplifier circuit of FIG.23A can be used to sense any charge stored in the DRAM cell 281 bycoupling the read bit line 289 to the V₁ terminal 656.

FIG. 129 is a cross-sectional view of an alternative embodiment of aDRAM cell 840, where similar reference numerals refer to like elements.In this example, the DRAM cell uses a fin-type capacitor 839. Thecapacitive fin 839 may be constructed in accordance with the disclosureset forth in application Ser. No. 08/366,786, filed Dec. 30, 1994, byAbe Yee, entitled METHOD OF MAKING MULTIPLE FIN CAPACITOR.

Memory Array Interconnect Architecture

The interconnection architecture of the present triangular DRAM cell 281has certain advantages as compared to prior art structures. Although thefollowing description focuses upon the illustrated example of a DRAMarray for convenience of explaination, the application of this aspect ofthe present invention is not limited to DRAM structures. With respect tothe present example, conventional memory arrays such as DRAMs and SRAMsare density limited by the metal pitch. The metal interconnect hasbecome a limiting feature inhibiting further shrinkage of the size ofthe layout.

In a conventional two layer memory array, the bit lines and the selectlines normally run on the same level of metal. As a result, as memorylayouts are made smaller and smaller, the bit lines and the select linesbecome closely packed. Wiring congestion, crosstalk, and parasiticcapacitance are problems limiting the performance and size ofconventional memory arrays. In the case of a DRAM cell, in particular,the line capacitance can be a problem when it becomes large relative tothe storage capacitance of the cell storage devices, for example storagecapacitor 283 shown in FIG. 23C. An operative design can only tolerate acertain ratio of line capacitance to storage capacitance. Conventionaldesigns are limited in the available options to deal with this problem.The only way to favorably adjust the ratio of storage capacitance toline capacitance was to increase the storage capacitance. The onlypractical way to increase the storage capacitance was to increase thesize of the cell. This had an adverse effect upon cell density, andlimits were imposed on how much a conventional memory cell could shrinkin size. Conventional memory structures were denied continued enjoymentof the many advantages that normally flow from further reducing the sizeof microelectronic structures.

In addition to size limitations, conventional DRAM layouts suffered fromperformance penalties. When designers were forced to increase thecapacitance of the cells in order to improve the ratio of storagecapacitance to line capacitance, they necessarily ran into limits uponhow much that capacitance could be increased. At some point, the amountof storage capacitance can become large enough to slow the speed of amemory array. Large amounts of capacitance take longer to charge anddischarge. In a sense amplifier circuit that must be precharged, it isnecessary to wait a sufficient amount of time before the circuitdesigner can be sure that the sensed voltage is valid. If a senseamplifier first reads a conductive cell and therefore discharges, thenswitches to another column, it may be necessary to wait until the columnhas enough time to charge. If the column being read has a nonconductivecell, the voltage sensed will gradually rise as the storage capacitanceis charged until it rises to a logic "one" level. The larger the amountof capacitance, the larger the RC time constant, and thus, the longer ittakes to charge the column. This slows the operation of the memorycircuit. The speed of microprocessors and other circuits has become sofast that memory accesses can be a significant limitation upon theperformance of the system. Access speeds are measured in nanoseconds.Thus, increased capacitance can be a problem with high performancememory circuits.

The triangular DRAM cell 281 is preferrably interconnected using thetri-directional routing arraingement described herein. The triangularDRAM cell 281 described herein allows for good use of three metal layertri-direction routing. The three layer metal routing layers allow groundconnections to be interconnected using the M3 metal layer, for example.The select lines 288 and 290 may be interconnected using the M2 metallayer, and the bit lines 287 and 289 may be implemented using the M1metal layer. The M3 layer is preferred for the ground connections, butthe other two metal layers may be used interchangeably for either thebit lines 287, 289 or the select lines 288, 290, as desired.

By routing select lines in a first metal layer, and bit lines in asecond metal layer, and power interconnect on a third metal layer,crosstalk is reduced. Line to line capacitance is reduced. Routingcongestion is reduced, permitting further shrinkage of the layout.Reduction in the size of the layout will result in reducing the totallength of wire and provide consequential performance improvements.

The advantages of the present DRAM interconnect system are alsoapplicable to an SRAM array described herein in connection with FIGS.24-28, and the SRAM array described in connection with FIGS. 21-22. Thismemory interconnect architecture described herein may be advantageouslyapplied to EPROM arrays, PROM arrays, ROM arrays, E² PROM arrays, flashEPROM arrays, and other circuit arraingements where cells are arraingedin a row by column matrix array.

An SRAM Array

FIG. 28 depicts a layout of an SRAM circuit which may be constructed inaccordance with the present invention. Portions of the layout are shownseparately in FIG. 24, FIG. 25, FIG. 26 and FIG. 27. The interconnectsystem described above with respect to a DRAM array is equallyapplicable to the SRAM array described. Of course, a three-by-threearray is described for purposes of illustration, but a practical circuitwould contain millions of such cells.

Referring to FIG. 24, a triangular structure 300 is depicted, which mayalso be referred to as a half cell 300. The half cell 300 has a firstdiffusion region 301. In this example, the first diffusion region 301 isa p diffusion region or PMOS island. A diffusion region 304 is shown inFIG. 24. In this example, the second diffusion region 304 is an ndiffusion region or NMOS island. Electrical connection may be made usingelectrode 307. Polysilicon layers 308 and 303 are shown. Localinterconnect 306 provides electrical connection between the region 304and the region 301. Similarly, local interconnect 302 and localinterconnect 305 are shown extending to the edge of the half cell 300and provide electrical connection with regions (not shown) in adjacenthalf cells.

A first transistor 294 is formed in the region where the polysilicon 308crosses the second diffusion region 304. The polysilicon layer 308 formsa gate electrode. An area of the second diffusion region 304 adjacent tothe polysilicon gate 308 is the drain region 299 of the transistor 294.A source region 298 of the transistor 294 is formed on the opposite sideof the gate electrode 308. The gate electrode 308 extends beyond theboundaries of the diffusion region 304 to provide electrical isolationbetween the source and drain regions 298 and 299, respectively. This issimilarly done for all the transistor structures shown in FIGS. 24-28.

A second transistor 295 is formed in the region where the polysilicon303 crosses the first diffusion region 301. The polysilicon layer 303forms a gate electrode for the second transistor 295. An area of thefirst diffusion region 301 adjacent to the polysilicon gate electrode303 is a drain region 297 of the transistor 295. A source region 296 ofthe transistor 295 is formed on the opposite side of the gate electrode303. Although the transistors formed will not be explicitly describedhereafter in every case, those skilled in the art will recognize thattransistors are formed where polysilicon layers cross diffusion regions.

Referring to FIG. 25, a first triangular structure 310 and a secondtriangular structure 311 are depicted, which together form a first typeof diamond shaped cell 312. A first diffusion region 313 is shown. Inthis example, the first diffusion region 313 is a p diffusion region. Asecond diffusion region 314 is shown. In this example, the seconddiffusion region 314 is an n diffusion region. Polysilicon 315 is formedover the second diffusion region 314 to form a gate electrode. Thus, atransistor is formed in the region where the polysilicon 315 crosses thesecond diffusion region 314. Polysilicon 316 is formed over the seconddiffusion region 314 and over the first diffusion region 313. Thispolysilicon 316 forms a gate electrode. Thus, transistors are formed inthe regions where the polysilicon 316 crosses the second diffusionregion 314 and where the polysilicon 316 crosses the first diffusionregion 313.

Transistors are also formed in the regions where polysilicon 317 crossesthe second diffusion region 314 and where the polysilicon 317 crossesthe first diffusion region 313. The polysilicon 317 is a common gateelectrode 317 for the two transistors that are thus formed. Apolysilicon layer 318 is shown extending from the edge of the secondtriangular shaped structure 312 to a region where it crosses the seconddiffusion region 314, at which region a transistor is formed. Thepolysilicon layer 318 provides electrical connection to structure in anadjacent half cell where it extends from the edge of the secondtriangular shaped half cell 312.

Local interconnect 322 establishes an electrical between the firstdiffusion region 313 and the second diffusion region 314. Localinterconnect 321 similarly establishes an electrical between the firstdiffusion region 313 and the second diffusion region 314. This area ofthe second diffusion region 314 is a common drain for two transistorsformed (a) where the polysilicon gate electrode 315 crosses the seconddiffusion region 314 , and (b) where the polysilicon gate electrode 316crosses the second diffusion region 314. Other local interconnects 320and 335 are shown in FIG. 25 extending to the edge of the cell 312 toprovide electrical connections to adjacent cells. Metal 323 is formed toprovide interconnection between the first diffusion region 313 and thepolysilicon common gate electrode 317.

A contact or via 332 is fabricated to facilitate electrical connection.Similarly, a contact or via 329 is also fabricated to facilitateelectrical connection. Electrical connection is provided between thefirst diffusion region 313 and the common gate electrode 316 by metal324. More specifically, the metal 324 is formed between contact 332 andcontact 329. The contact 329 is electrically connected to localinterconnect 322. The contact 332 is electrically connected to thecommon gate electrode 316.

A contact or via 331 provides electrical connection with the seconddiffusion region 314. Metal 325 provides electrical connection with thecontact 331 to provide an output terminal or via 334 to facilitateelectrical connection with other interconnect layers (not shown) whichmay be fabricated in later manufacturing steps. Metal 326 provideselectrical connection between a contact 327 (which is in electricalconnection with the second diffusion layer 314) and an output terminalor via 333.

Contacts 336 and 337 are partially shown in FIG. 25. These contacts 336and 337 are partially located on adjacent cells which are not shown inFIG. 25. A diffusion region 319 of the same type as the second diffusionregion 314 is fabricated below the local interconnect 320 and thecontact 337 which is partially shown in FIG. 25. A diffusuin region ofthe same type as the first diffusion region 313 is formed below thelocal interconnect 335 and the contact 336, which is partially shown inFIG. 25.

FIG. 26 shows a second type of diamond shaped cell 340 comprising afirst half cell 341 and a second half cell 342. A first diffusion region343 and a second diffusion region 344 are p-type diffusion regions. Athird diffusion region 345 and a fourth diffusion region 346 are n-typediffusion regions. Polysilicon 347, 348 and 349 form gate electrodes. Asdiscribed above, transistors are formed where the polysilicon 347, 348and 349 cross the diffusion regions 343, 344, 345 and 346.

Local interconnect 350, 351, 352, 357 and 366 is used to make electricalconnections with certain parts of the circuit, as shown in FIG. 26.Metal 353 and 354 also make certain electrical connections, and metal355 forms a terminal 356. Vias 358, 359, 360 and 361 are provided tofacilitate electrical connections between layers. Vias 362, 363 and 364are partially shown in FIG. 26, and extend to adjacent cells (notshown). Terminal 365 is provided to facilitate external connection tothe cell 340. A diffusion region 367 is shown below the localinterconnect 357. A diffusion region 368 is shown below the localinterconnect 366. The diffusion regions 367 and 368 are p-type diffusionregions. A diffusion region 369 is formed below local interconnect 352.The diffusion region 369 is an n-type diffusion region.

FIG. 27 shows a third type of cell 370. The third type of cell 370comprises a first half cell 371 and a second half cell 372. A firstdiffusion region 373 and a second diffusion region 374 are p-typediffusion regions. Additional n-type diffusion regions 377 and 378 areshown. An additional n-type diffusion region 379 is also shown.Polysilicon 397, 398 and 399 form gate electrodes and provide certaininterconnections as shown.

Local interconnect 380, 381, 382, 383 and 384 is used to make electricalconnections with certain parts of the circuit, as shown in FIG. 27.Local interconnect 382 is formed over the diffusion region 378. Localinterconnect 384 is formed over the diffusion region 377. And localinterconnect 383 is formed over the diffusion region 379. Metal 385 and386 also make certain electrical connections, and metal 387 forms aterminal 388. Vias 389, 390, 391 and 393 are provided to facilitateelectrical connections between layers. Terminal 392 is provided tofacilitate external connection to the cell 340. Vias 394, 395 and 396are partially shown in FIG. 27, and extend to adjacent cells (notshown).

The three types of cells 312, 340 and 370 are combined to form thememory circuit 400 shown in FIG. 28. In addition, FIG. 28 shows a powerline connection 402 and a power connection 403, which comprise metallayer interconnect. Ground connections 401 and 404 comprise metal layerconnections. Adjacent cells have common power connections. Common groundconnections are also provided for adjacent cells.

A bit line 405 is similarly formed by metal layer interconnect. Terminal334 provides electrical connection between bit line 405 and associatedcircuitry of the first type of cell 312. A bit line bar 406 provides thecomplement of data available on the bit line 405. Terminal 333 provideselectrical connection between bit line bar 406 and associated circuitryof the first type of cell 312. A first address line or select line 407is formed from metal interconnect. A second address line or select line408 and a third address line 409 are also illustrated.

It will be noted that six closely packed half cells 311, 310, 341, 342,371, and 372 define a larger parallelogram cell 400, and may also definea hexagonal shape. This relationship can be used within the scope of theinvention to provide larger unit cells having parallelogram or hexagonalshapes defined by closely packed triangular shaped half cells 311, 310,341, 342, 371, and 372, with internal structures similar to or differentfrom those which are explicitly described and illustrated. In such anarrangement, the parallelogram or hexagon unit cells can be consideredto be the basic building block.

The SRAM array 400 is shown interconnected using the tri-directionalrouting arraingement described herein. The illustrated SRAM array 400described herein allows for good use of three metal layer tri-directionrouting. The three layer metal routing layers allow ground connections401 and 404, power connections 402 and 403, and bit lines 405 and 406,to be interconnected using the M3 metal layer, for example. The addressselect lines 407, 408 and 409 may be interconnected using the M2 metallayer. Note that in this embodiment, all three routing directions areused in the M2 metal layers. The metal connections described above withrespect to FIGS. 24, 25, 26 and 27 may be implemented using the M1 metallayer.

By routing address select lines 407, 408 and 409 in the second metallayer, and bit lines 405 and 406 in the third metal layer, along withthe power interconnect 402 and 403, and ground connections 401 and 404,crosstalk is reduced. Line to line capacitance is reduced. The totallength of wire is reduced. Routing congestion is reduced, permitting alayout that is compact and that can be squeezed into minimal real estateon a semiconductor die.

Dies

Modern integrated circuits are generally produced by creating severalidentical integrated circuit dies at individual die sites on a singlesemiconductor wafer, then scribing (slicing) the wafer to separate thedies from one another. Circuits and active elements on the dies arefabricated while the dies are still together on the wafer by ionimplantation, electron beam lithography, plasma etching, mechanicalpolishing, sputtering, and other steps known to those skilled in theart.

In the present invention, the number of individual dies of a given areathat can be laid out on a single semiconductor wafer may be increased insome instances by using hexagonal shaped die, or triangular shaped die,or diamond shaped die. This may reduce the wasted real estate on awafer, thus increasing the wafer-layout-efficiency.

Also, 1,1,1 silicon may be advantageously used in some instances, suchas diamond shaped die, because the structure breaks easily or is easierto scribe in certain directions.

CAD For Hexagonal Architecture

Present computer aided design (CAD) systems for the design of electroniccircuits, referred to as ECAD or Electronic CAD systems, assist in thedesign of electronic circuits by providing a user with a set of softwaretools running on a digital computer with a graphical display device.Typically, five basic software program functions are required for anECAD system: a schematic editor, a logic compiler, a logic simulator, alogic verifier, and a layout program. The schematic editor programallows the user of the system to enter and/or modify a schematic diagramusing the display screen, generating a net list (summary of connectionsbetween components) in the process. The logic compiler takes the netlist as an input, and using a component database puts all of theinformation necessary for layout, verification and simulation into aschematic object file or files whose format(s) is (are) optimizedspecifically for those functions. The logic verifier checks theschematic for design errors, such as multiple outputs connectedtogether, overloaded signal paths, etc., and generates error indicationsif any such design problems exist. The logic simulator takes theschematic object file(s) and simulation models, and generates a set ofsimulation results, acting on instructions initial conditions and inputsignal values provided to it either in the form of a file or user input.The layout program generates data from which a semiconductor chip (or acircuit board) may be laid out and produced. In more advanced systems,the schematic is replaced by a higher-level Hardware DescriptionLanguage (HDL) and a logic synthesizer creates the netlist. The othersteps are basically the same.

The Concurrent Modular Design Environment (CMDE®) produced by LSI LogicCorporation of Milpitas, Calif. is a suite of software tools forcomputers running the UNIX operating system. CMDE software comprises aschematic editor (LSED®) and a simulator (LDS®), among other softwareprograms, and provides an example of commercially available tools of theaforementioned type. Other examples of a schematic editor, schematiccompiler, and schematic simulator may be found in systems produced byMentor Graphics of Beaverton, Oreg. and Cadence Design Systems of SanJose, Calif. (successors to Valid Logic Systems, Inc. of Mountain View,Calif., who produced the SCALD station).

VHDL, or VHSIC (Very High Speed Integrated Circuit) Hardware DescriptionLanguage, is a recently developed, higher level language for describingcomplex devices. The form of a VHDL or most other Hardware DesignLanguage (HDL) description is described by means of a context-freesyntax together with context-dependent syntactic and semanticrequirements expressed by narrative rules.

A methodology for deriving a lower-level, physically-implementabledescription, such as a RTL description of the higher level (e.g. VHDL)description useful for CAD design of the present invention is shown inU.S. Pat. No. 5,222,030, issued Jun. 22, 1993, by Dangelo et al.,entitled METHODOLOGY FOR DERIVING EXECUTABLE LOW-LEVEL STRUCTURALDESCRIPTIONS AND VALID PHYSICAL IMPLEMENTATIONS OF CIRCUITS AND SYSTEMSFROM HIGH-LEVEL SEMANTIC SPECIFICATIONS AND DESCRIPTIONS THEREOF, whichis incorporated herein by reference. Additional related descriptionsappear in application Ser. No. 08/076,738, filed Jun. 14, 1993, byRostoker et al., entitled AREA AND POWER ESTIMATION FOR ELECTRONICDESIGNS FROM HIGH-LEVEL SEMANTIC SPECIFICATIONS AND DESCRIPTION, andapplication Ser. No. 08/076,729, filed Jun. 14, 1993, by Rostoker etal., entitled CONSTRAINT-DRIVEN PARTITIONING OF ELECTRONIC DESIGNS FROMHIGH-LEVEL SEMANTIC SPECIFICATIONS AND DESCRIPTIONS, both of which areincorporated herein by reference. Traditionally, some form of CAD systemis used to develop the placement and routing, or floorplanning, of themicroelectronic integrated circuit (IC), whether at high level (i.e.HDL) or lower level (i.e. RTL) or other abstraction.

Microelectronic integrated circuits consist of a large number ofelectronic components that are fabricated by layering several differentmaterials on a silicon base or wafer. The design of an integratedcircuit transforms a circuit description into a geometric descriptionwhich is known as a layout. A layout consists of a set of planargeometric shapes in several layers.

The layout is then checked to ensure that it meets all of the designrequirements. The result is a set of design files in a particularunambiguous representation known as an intermediate form that describesthe layout. The design files are then converted into pattern generatorfiles that are used to produce patterns called masks by an optical orelectron beam pattern generator.

During fabrication, these masks are used to pattern a silicon or othersemiconductor (such as Gallium Arsenide, etc.) wafer using a sequence ofphotolithographic steps. The component formation requires very exactingdetails about geometric patterns and separation between them. Theprocess of converting the specifications of an electrical circuit into alayout is called the physical design. It is an extremely tedious and anerror-prone process because of the tight tolerance requirements, thecomplexity of the physical design rules, and the minuteness of theindividual components.

Currently, the minimum geometric feature size of a component is on theorder of 0.5 microns. However, it is expected that the feature size canbe reduced to 0.1 micron within several years. This small feature sizeallows fabrication of as many as 4.5 million transistors or 1 milliongates of logic on a 25 millimeter by 25 millimeter chip. This trend isexpected to continue, with even smaller feature geometries and morecircuit elements on an integrated circuit, and of course, larger die (orchip) sizes will allow far greater numbers of circuit elements with theadvent of the instant invention for triangular transistor structures andtriangular, parallelogram, diamond or hexagonal gates, cells of otherstructures on a die, even larger numbers of circuit elements should becapable of being fabricated on an integrated circuit.

Due to the large number of components and the exacting details requiredby the fabrication process, physical design is not practical without theaid of computers. As a result, most phases of physical designextensively use Computer Aided Design (CAD) tools, and many phases havealready been partially or fully automated. Automation of the physicaldesign process has increased the level of integration, reduced turnaround time and enhanced chip performance.

The objective of physical design is to determine an optimal arrangementof devices in a plane or in a three dimensional space, and an efficientinterconnection or routing scheme between the devices to obtain thedesired functionality. Since space on a wafer is very expensive realestate, algorithms must use the space very efficiently to lower costsand improve yield.

An exemplary integrated circuit chip is illustrated in FIG. 91 andgenerally designated by the reference numeral 4000. Although the chipdie is shown as a rectangular (near-square) configuration, it may infact be a non-square die configuration. Actually, hexagonal,parallelogram, rhomboidal, diamond and triangular cells may fit better(tile more completely) into certain non-square die shapes, especiallyparallelogram, rhomboidal and triangular die. Suitable non-square dieare shown in U.S. Pat. No. 5,341,024, issued Aug. 23, 1994, by Rostoker,entitled METHOD OF INCREASING THE LAYOUT EFFICIENCY OF DIES ON A WAFERAND INCREASING THE RATIO OF I/O AREA TO ACTIVE AREA PER DIE; and U.S.Pat. No. 5,300,815, issued Apr. 5, 1994, by Rostoker, entitled TECHNIQUEOF INCREASING BOND PAD DENSITY ON A SEMICONDUCTOR DIE, both of which areincorporated herein by reference. Packaging of such non-square die isshown in U.S. Pat. No. 5,329,157, issued Jul. 12, 1994, by Rostoker,entitled SEMICONDUCTOR PACKAGING TECHNIQUE YIELDING INCREASED INNER LEADCOUNT FOR A GIVEN DIE- RECEIVING AREA, the entire disclosure of which isincorporated herein by reference. CAD layout floorplanning fornon-square die is shown in application Ser. No. 07/958,208, filed Oct.7, 1992, by Rostoker, entitled VARIABLE DIE SHAPE FLOORPLANNING, nowU.S. Pat. No. 5,340,772, issued Aug. 23, 1994; application Ser. No.08/016,864, filed Feb. 10, 1993, by Rostoker, entitled FLOORPLANNINGTECHNIQUE USING LOW ASPECT-RATIO PARTITIONING; and application Ser. No.08/015,947, filed Feb. 10, 1993, by Rostoker, entitled FLOORPLANNINGTECHNIQUE USING MULTI-PARTITIONING, all of which are incorporated hereinby reference.

The integrated circuit die 4000 includes a semiconductor substrate 4002on which are formed a number of functional circuit blocks that can havedifferent sizes and shapes. Some blocks are relatively large, such assquare blocks 4004 and 4006, rectangular blocks 4008 and 4010,triangular blocks 4012 and 4014, diamond blocks 4016 and 4018,parallelogram blocks 4020, 4021 and 4022, rhomboidal blocks 4024 and4026, and hexagonal blocks 4028 and 4030. Each of the large blocks 4006,4010, 4014, 4016, 4021, 4022, 4026, and 4030; are shown in schematicform and as a schematic made up of smaller triangular block segments, asby smaller triangular cells or triangular transistors. Such largerblocks may be made up of a group of other shapes, such as a group ofhexes forming block 4029. And older, more traditional larger blocks like4041 may be made up of smaller square blocks 4042. Also, as otherexamples, irregular larger block 4005 is shown made up of parallelogramblocks 4007 and irregular larger block 4009 is made up of rhomboidalblocks 4011; while regular larger rectangular block 4013 is made up ofrectangles 4015 (each of which is similar to rectangular block 4008) andirregular block 4029 is made up of closely spaced hexagonal blocks 4032.

Such larger blocks may represent the outline of logic or memoryfunctions, such as a central processing unit (CPU) or memory cell (suchas RAM, ROM, EPROM) or the like. Alternatively, smaller blocks, such asclosely spaced hexes 4032 or widely spaced hexes 4034 as well as closelyspaced triangles 4036 and widely spaced triangles 4038 may be used withor instead of the more traditional square or near-square small blockswhich may be widely spaced 4040 or closely spaced 4042. Input/output(I/O) pads, such as bond pads, for communicating signals and power ontoor off from the die 4000 may also have non-square configurations asshown by triangular I/O pads 4044, hexagonal I/O pads 4046,parallelogram I/O pads 4048, rhomboidal I/O pads 4050, and diamondshaped I/O pads which, uniformly or in combination, may be used inconjunction with or to replace the more traditional square ornear-square I/O pads 4054. Even with advances in angled or shaped I/Opads as shown in U.S. Pat. No. 5,300,815, issued Apr. 5, 1994, byRostoker, entitled TECHNIQUE OF INCREASING BOND PAD DENSITY ON ASEMICONDUCTOR DIE (previously noted), herein shown in FIG. 91 at 4056,I/O pads may be selectively replaced with I/O pads of the currentinvention, as by angled parallelogram I/O pads 4058, angled triangularpads 4060 or angled rhomboidal pads 4062 or the like. Any of these I/Opads may be on the periphery or interior of the die 4000 area and may beused as for electrical contact in wire bonding, Tape AutomatedBonding(TAB), Flip chip (see U.S. Pat. No. 5,399,898, issued Mar. 21,1995, by Rostoker, entitled MULTI-CHIP SEMICONDUCTOR ARRANGEMENTS USINGFLIP CHIP DIES, which is incorporated herein by reference) or otherconnection means known to one of skill in the art. These blocks4004-4062 can be considered as modules for use in various circuitdesigns, and may be represented as standard designs in circuitlibraries.

The integrated circuit 4000 may therefore comprise multiple largerblocks along with a large number, which can be tens of thousands,hundreds of thousands or even millions or more of small cells such asblocks 4030-4042. Each cell whether separate as with 4030-4042 orcombined into larger blocks, such as 4006, 4010, 4014, 4021, 4022, 4030and 4036 represents a single logic element, such as a gate, or severallogic elements that are interconnected in a standardized manner toperform a specific function. Cells that consist of two or moreinterconnected gates or logic elements are also available as standardmodules in circuit libraries.

The cells and other elements of the circuit die 4000 described above areinterconnected or routed in accordance with the logical design of thecircuit to provide the desired functionality. Although not visible inthe drawing, the various elements of the circuit die 4000 areinterconnected by electrically conductive lines or traces that arerouted, for example, through 90 degree intersecting vertical channels4066 and horizontal channels 4068 that run between the square cells 4040or by sixty degree intersecting channels 4070, 4072 and 4074 that runbetween the triangular cells 4038 and the hexagonal cells 4034 and thelike. Alternatively, conductive lines for interconnect may be routedover the top or side of any or a plurality of cells (not shown) insteadof or in conjunction with the channeled interconnect method.

The input to the physical design problem is a circuit diagram orspecific characteristics (as in the case of an HDL description) and theoutput is the layout of the circuit. This is accomplished in severalstages including partitioning, floor planning, placement, routing andcompaction.

Partitioning--A chip may contain several million transistors. Layout ofthe entire circuit cannot traditionally be handled due to the limitationof memory space as well as the computation power available. Therefore itis normally partitioned by grouping the components into blocks such assubcircuits and modules. The actual partitioning process considers manyfactors such as the size of the blocks, number of block and number ofinterconnections between the blocks.

The output of partitioning is a set of blocks, along with theinterconnections required between blocks. The set of interconnectionsrequired is commonly referred to as a netlist. In large circuits, thepartitioning process is often hierarchical, although non-hierarchical(e.g. flat) processes can be used, and at the topmost level a circuitcan have between 5 to 25 blocks. However, greater numbers of blocks arepossible and contemplated. Each block is then partitioned recursivelyinto smaller blocks.

Floor planning and placement--This step is concerned with selecting goodlayout alternatives for each block of the entire chip, as well asbetween blocks and to the edges. Floor planning is a critical step as itsets up the ground work for a good layout. However it is computationallyquite hard. Very often the task of floor plan layout is done by a designengineer using a CAD tool. This is necessary as the major components ofan IC are often intended for specific locations on the IC die.

Only for simple layouts can the current layout tools provide a solutionwithout human-engineering direction and intervention. One aspect of thepresent invention will permit complex problems, including flow planlayout, to be accomplished without regular human intervention.

During placement, the blocks are exactly positioned on the die. The goalof placement is to find a minimum area arrangement for the blocks thatallows completion of interconnections between the blocks. Placement istypically done in two phases. In the first phase, an initial placementis created. In the second phase, the initial placement is evaluated anditerative improvements are made until the layout has minimum area andconforms to design specifications.

The 90 degree intersecting vertical and horizontal channels 4066 and4068 or alternatively the 60 degree intersecting channels 4070, 4072 and4074 are generally provided between the blocks in order to allow forelectrical interconnections. The quality of the placement will not beevident until the routing phase has been completed. A particularplacement may lead to an unroutable design. For example, routing may notbe possible in the space provided. In that case another iteration ofplacement is necessary. Sometimes routing is implemented over the entirearea, including over some or all of the blocks, and not just over thechannels.

To limit the number of iterations of the placement algorithm, anestimate of the required routing space is used during the placementphase. A good routing and circuit performance heavily depend on a goodplacement algorithm. This is due to the fact that once the position ofeach block is fixed, very little can be done to improve the routing andoverall circuit performance.

Routing--The objective of the routing phase is to complete theinterconnections between blocks according to the specified netlist.First, the space not occupied by blocks, which is called the routingspace, is partitioned into rectangular regions called channels andswitch boxes. The goal of a router is to complete all circuitconnections using the shortest possible wire length and using only thechannel and switch boxes.

Routing is usually done in two phases referred to as the global routingand detailed routing phases. In global routing, connections arecompleted between the proper blocks of the circuit disregarding theexact geometric details of each wire and terminal. For each wire, aglobal router finds a list of channels that are to be used as apassageway for that wire. In other words, global routing specifies theloose route of a wire through different regions of the routing space.

Global routing is followed by detailed routing which completespoint-to-point connections between terminals on the blocks. Looserouting is converted into exact routing by specifying the geometricinformation such as width of wires and their layer assignments. Detailedrouting includes channel routing and switch box routing.

Due to the nature of the routing algorithms, complete routing of allconnections cannot be guaranteed in many cases. As a result, a techniquecalled "rip up and re-route" is used that removes troublesomeconnections and re-routes them in a different order. One suitablerouting system is disclosed and described in application Ser. No.08/131,770, by Scepanovic, et al., filed Oct. 4, 1993, entitled TOWARDSOPTIMAL STEINER TREE ROUTING IN THE PRESENCE OF RECTILINEAR OBSTACLES,which is incorporated herein by reference.

Compaction--Compaction is the task of compressing the layout in alldirections such that the total area is reduced. By making the chips(each IC die) smaller, wire lengths are reduced which in turn reducesthe signal delay between components of the circuit. At the same time asmaller area enables more IC die to be produced on a wafer which in turnreduces the cost of manufacturing. Compaction must ensure that no rulesregarding the design and fabrication process are violated.

Very Large Scale Integration (VLSI) physical design is iterative innature and many steps such as global routing and channel routing arerepeated several times to obtain a better layout. In addition, thequality of results obtained in one stage depends on the quality ofsolution obtained in earlier stages as discussed above. For example, apoor quality placement cannot be fully cured by high quality routing. Asa result, earlier steps have extensive influence on the overall qualityof the solution.

In this sense, partitioning, floor planning and placement problems playa more important role in determining the area and chip performance incomparison to routing and compaction. Since placement may produce anunroutable layout, the chip might need to be re-placed or re-partitionedbefore another routing is attempted. The whole design cycle isconventionally repeated several times to accomplish the designobjectives. The complexity of each step varies depending on the designconstraints as well as the design style used.

The area of the physical design problem to which an aspect of thepresent invention relates is the placement and routing of the blocks(including cells and I/O pads) and other elements on the integratedcircuit 4000 illustrated in FIG. 91. After the circuit partitioningphase, the area occupied by each block (4004-4054 and 4060-4062) can becalculated, and the number of teminals required by each block is known.In addition, the netlists specifying the connections between the blocksare also specified.

In order to complete the layout, it is necessary to arrange the blockson the layout surface and interconnect their terminals according to thenetlist. The arrangement of blocks is done in the placement phase whileinterconnection is completed in the routing phase. In the placementphase, the blocks are assigned a specific shape and are positioned on alayout surface in such a fashion that no two blocks are overlapping andenough space is left on the layout surface to complete interconnectionsbetween the blocks. The blocks are positioned so as to minimize thetotal area of the layout. In addition, the locations of the terminals oneach block are also determined.

Physical Design Algorithms

a. Overview

Very Large Scale Integration (VLSI) Integrated Circuit (IC) physicaldesign automation utilizes algorithms and data structures related to thephysical design process. A general treatise on this art is presented ina textbook entitled "Algorithms for VLSI Physical Design Automation" byNaveed Sherwani, Kluwer Academic Publishers 1993, incorporated herein byreference.

Depending on the input, placement algorithms can be classified into twomajor groups, constructive placement and iterative improvement methods.The input to the constructive placement algorithms consists of a set ofblocks along with the netlist. The algorithm finds the locations of theblocks. On the other hand, iterative improvement algorithms start withan initial placement. These algorithms modify the initial placement insearch of a better placement. The algorithms are applied in a recursiveor an iterative manner until no further improvement is possible, or thesolution is considered to be satisfactory based on a predeterminedcriteria.

Iterative algorithms can be divided into three general classifications,simulated annealing, simulated evolution and force directed placement.The simulated annealing algorithm simulates the physical annealingprocess that is used to temper metals. Simulated evolution simulates thebiological process of evolution, while the force directed placementsimulates a system of bodies attached by springs.

Assuming that a number N of cells are to be optimally arranged androuted on an integrated circuit chip, the number of different ways thatthe cells can be arranged on the chip, or the number of permutations, isequal to N| (N factorial). In the following description each arrangementof cells will be referred to as a placement. In a practical integratedcircuit chip (die), the number of cells can be hundreds of thousands ormillions. Thus, the number of possible placements is extremely large.

Iterative algorithms function by generating large numbers of possibleplacements and comparing them in accordance with some criteria which isgenerally referred to as fitness. The fitness of a placement can bemeasured in a number of different ways, for example, overall chip size.A small size is associated with a high fitness and vice versa. Anothermeasure of fitness is the total wire length of the integrated circuit. Ahigh total wire length indicates low fitness and vice versa.

The relative desirability of various placement configurations canalternatively be expressed in terms of cost, which can be considered atthe inverse of fitness, with high cost corresponding to low fitness andvice versa.

b. Simulated Annealing

Basic simulated annealing per se is well known in the art and has beensuccessfully used in many phases of VLSI physical design such as circuitpartitioning. Simulated annealing is used in placement as an iterativeimprovement algorithm. Given a placement configuration, a change to thatconfiguration is made by moving a component or interchanging locationsof two components. Such interchange can be alternatively expressed astransposition or swapping.

In the case of a simple pairwise interchange algorithm, it is possiblethat a configuration achieved has a cost higher than that of theoptimum, but no interchange can cause further cost reduction. In such asituation, the algorithm is trapped at a local optimum and cannotproceed further. This happens quite often when the algorithm is used inpractical applications. Simulated annealing helps to avoid getting stuckat a local optima by occasionally accepting moves that result in a costincrease.

In simulated annealing, all moves that result in a decrease in cost areaccepted. Moves that result in an increase in cost are accepted with aprobability that decreases over the iterations. The analogy to theactual annealing process is heightened with the use of a parametercalled temperature ("T"). This parameter controls the probability ofaccepting moves that result in increased cost.

More of such moves are accepted at higher values of temperature than atlower values. The algorithm starts with a very high value of temperaturethat gradually decreases so that moves that increase cost have aprogressively lower probability of being accepted. Finally, thetemperature reduces to a very low value which requires that only movesthat reduce costs are to be accepted. In this way, the algorithmconverges to an optimal or near optimal configuration.

In each stage, the placement is shuffled randomly to get a newplacement. This random shuffling could be achieved by transposing a cellto a random location, a transposition of two cells, or any other movethat can change the wire length or other cost criteria. After theshuffle, the change in cost is evaluated. If there is a decrease incost, the configuration is accepted. Otherwise, the new configuration isaccepted with a probability that depends on the temperature.

The temperature is then lowered using some function which, for example,could be exponential in nature. The process is stopped when thetemperature is dropped to a certain level. A number of variations andimprovements on the basic simulated annealing algorithm have beendeveloped. An example is described in an article entitled "Timberwolf3.2 A New Standard Cell Placement and Global Routing Package" by CarlSechen, et al. IEEE 23rd Designed Automation Conference paper 26.1,especially at pages 432 to 439, and this entire article is incorporatedherein by reference.

c. Simulated Evolution

Simulated evolution, which is also known as the genetic algorithm, isanalogous to the natural process of mutation of species as they evolveto better adapt to their environment. The algorithm starts with aninitial set of placement configurations which is called the population.The initial placement can be generated randomly. The individuals in thepopulation represent a feasible placement to the optimization problemand are actually represented by a string of symbols.

The symbols used in the solution string are called genes. A solutionstring made up of genes is called a chromosome. A schema is a set ofgenes that make up a partial solution. The simulated evolution orgenetic algorithm is iterated, and each iteration is called ageneration. During each iteration, the individual placements of thepopulation are evaluated on the basis of fitness or cost. Two individualplacements among the population are selected as parents, withprobabilities based on their fitness. The better fitness a placementhas, the higher the probability that it will be chosen.

The genetic operators called crossover, mutation and inversion, whichare analogous to their counterparts in the evolution process, areapplied to the parents to combine genes from each parent to generate anew individual called the offspring or child. The offspring areevaluated, and a new generation is formed by including some of theparents and the offspring on the basis of their fitness in a manner suchthat the size of the population remains the same. As the tendency is toselect high fitness individuals to generate offspring, and the weakindividuals are deleted, the next generation tends to have individualsthat have good fitness.

The fitness of the entire population improves over the generations. Thatmeans that the overall placement quality improves over iterations. Atthe same time, some low fitness individuals are reproduced from previousgenerations to maintain diversity even though the probability of doingso is quite low. In this way, it is assured that the algorithm does notget stuck at some local optimum.

The first main operator of the genetic algorithm is crossover, whichgenerates offspring by combining schemata of two individuals at a time.This can be achieved by choosing a random cut point and generating theoffspring by combining the left segment of one parent with the rightsegment of the other. However, after doing so, some cells may beduplicated while other cells are deleted. This problem will be describedin detail below.

The amount of crossover is controlled by the crossover rate, which isdefined as the ratio of the number of offspring produced by crossing ineach generation to the population size. Crossover attempts to createoffspring with fitness higher than either parent by combining the bestgenes from each.

Mutation creates incremental random changes. The most commonly usedmutation is pairwise interchange or transposition. This is the processby which new genes that did not exist in the original generation, orhave been lost, can be generated.

The mutation rate is defined as the ratio of the number of offspringproduced by mutation in each generation to the population size. It mustbe carefully chosen because while it can introduce more useful genes,most mutations are harmful and reduce fitness. The primary applicationof mutation is to pull the algorithm out of local optima.

Inversion is an operator that changes the representation of a placementwithout actually changing the placement itself so that an offspring ismore likely to inherit certain schema from one parent.

After the offspring are generated, individual placements for the nextgeneration are chosen based on some criteria. Numerous selectioncriteria are available, such as total chip size and wire length asdescribed above. In competitive selection, all the parents and offspringcompete with each other, and the fittest placements are selected so thatthe population remains constant. In random selection, the placements forthe next generation are randomly selected so that the population remainsconstant.

The latter criteria is often advantageous considering the fact that byselecting the fittest individuals, the population converges toindividuals that share the same genes and the search may not converge toan optimum. However, if the individuals are chosen randomly there is noway to gain improvement from older generation to new generation. Bycombining both methods, stochastic selection make selections withprobabilities based on the fitness of each individual.

d. Force Directed Placement

Force directed placement exploits the similarity between the placementproblem and the classical mechanics problem of a system of bodiesattached to springs. In this method, the blocks connected to each otherby nets are supposed to exert attractive forces on each other. Themagnitude of this force is directly proportional to the distance betweenthe blocks. Additional proportionality is achieved by connecting more"springs" between blocks that "talk" to each other more (volume,frequency, etc.) And fewer "springs" where less extensive communicationoccurs between each block.

According to Hooke's Law, the force exerted due to the stretching of thesprings is proportional to the distance between the bodies connected tothe spring. If the bodies are allowed to move freely, they would move inthe direction of the force until the system achieved equilibrium. Thesame idea is used for placing the cells. The final configuration of theplacement of cells is the one in which the system achieves a solutionthat is closest to or in actual equilibrium.

A description and disclosure of a system and methodology for developingan integrated circuit cell placement representation using physicaldesign algorithms as discussed above is set out in application Ser. No.08/229,826, filed Apr. 19, 1994, by Rostoker et al., entitled INTEGRATEDCIRCUIT PHYSICAL DESIGN AUTOMATION SYSTEM UTILIZING OPTIMIZATION PROCESSDECOMPOSITION AND PARALLEL PROCESSING, the entire disclosure of which isincorporated herein by reference.

More specifically, in light of the present invention, floorplanning isthe process of placing functional devices ("functions," also referred toas modules, elements, blocks, or functional blocks) on a chip(integrated circuit die), and allocating interconnection space amongthem so as to minimize the actual chip area required to encompass suchfunctions and their interconnections, and to maximize the probabilitythat such interconnections can be routed within that area.

Related to the floorplanning process, and creating a competing need forchip or die area is the amount of input/output (I/O) space required bythe functional devices. Bond pads (connection points to the die) and therelatively large driver/receiver circuits and static protection networksrequired for input and output connections require a significant portionof the perimeter area of in integrated circuit die (chip) and eat intothe space available for placing other functional devices.

Prior to the floorplanning process itself, which involves the placementof functions on a chip, the chip's logic must be designed. Logicdesigners generally employ hierarchical design techniques to determinethe appropriate selection and interconnection of logic and/or memorydevices which will enable the chip to perform the desired function.These techniques involve describing the chip's functionality at various"levels of abstraction," ranging from the most general functionperformed by the chip to the precise functions performed by each logicand/or memory element on the chip.

Thus, a logic designer's hierarchy consists of N levels of functions,where N is an integer (N≧1) representing the number of hierarchicallevels of functionality in the chip, the first level being the chipitself, and where n is an integer (1≦n≦N) representing the level of anyparticular function in the hierarchy.

A "parent" function at the (n)th level of the hierarchy is defined as aplurality of (n+1)^(st) level "children" functions, each of which is a"child" function. For example, a microprocessor at the (n)th level mightbe defined as the parent of the following (n+1)^(st) level children: anALU, a series of registers, a bus and various other functions (each ofwhich may or may not have a plurality of (n+2)^(nd) level children, andso on).

Each child function which is not also a parent function (i.e., which hasno children) is referred to as a "terminal" (or "leaf") function. Eachterminal function is connected to at least one other terminal function,such connection commonly being referred to as a "net". A series of nets,each of which defines a plurality of interconnected functions, iscommonly referred to as a "net list."

Note that lower levels of the hierarchy are commonly denoted bysuccessively higher numbers. Thus, while level 1 refers to the top(chip) level of the hierarchy, levels 2, 3, and 4 constitutesuccessively "lower" levels of the hierarchy.

Automated techniques for floorplanning ("floorplanners") are known inthe prior art and fall into three basic categories: (1) "flat"floorplanners, which attempt to minimize space at only one level (the"level" which is created when the hierarchy is flattened by omitting allbut the terminal functions), by placing only terminal functions; (2)"top-automated" floorplanners, which automate the floorplanning processat only the top level by placing only second level functions; and (3)"hierarchical" floorplanners, which automates the process offloorplanning by optimizing placement of functions at many levels(preferably, at all levels).

An example of a hierarchical floorplanner which operates at all levelsof hierarchy is taught in U.S. Pat. No. 4,918,614, issued Apr. 17, 1990,to Modarres et. al., and assigned to LSI Logic Corporation of Milpitas,Calif., which is incorporated herein by reference. Further referencescited in U.S. Pat. No. 4,918,614 describe various "flat" floorplanners,and floorplanning related techniques.

Modern integrated circuits are generally produced by creating severalidentical integrated circuit dies at individual "die sites" on a singlesemiconductor wafer, then scribing (slicing) the wafer to separate(singulate, dice) the dies from one another. Generally, the dies areeither rectangular or square. On the other hand, semiconductor wafersare generally round. The prior art die sites are defined by a series ofparallel scribe lines which extend chordwise across the wafer,perpendicular to another series of chordwise parallel scribe lines.

Circuits and active elements on the dies are created while the dies arestill together (un-singulated) on the wafer by ion deposition, electronbeam lithography, plasma etching, mechanical polishing, sputtering, andnumerous other methods which are well known to those skilled in the artof semiconductor fabrication. These processes are highly developed andare capable of producing extremely complicated circuits on the dies at arelatively low cost. However, the prior art method of fabricating squareor rectangular "die sites" from a semiconductor wafer is impeding thedevelopment of complex integrated circuit dies. Problems with the priorart include (1) low wafer-layout-efficiency, E_(W), and (2) lowdie-topology-efficiency, E_(D). Non-square die configurations havesolved certain of these problems, as noted previously. However, in arelated conception traditionally rectangular arrays of square orrectangular blocks have been developed to fit on the traditionallysquare die.

FIG. 92A shows a prior art block 4100 of near square or square sub blockcells 4102a, 4102b, 4102c-4102ii, 4102jj and 4102kk. The blocks 4102 areseparated by vertical lines 4104a-4104h and by horizontal line4106a-4106h. The lines 4104 and 4106 may act as routing channels in awidely spaced configuration (as like the blocks 4040 FIG. 91 separatedby vertical channels 4066 and horizontal channels 4068, respectively ormerely as reference lines noting the demarcation of each sub-block 4102(which may be considered a block in itself).

FIG. 92B shows an exemplar prior art square of near square block (orsub-block) of simple construction generally designated by the number4150. Block 4150 may represent any square or near square block orsub-block as, for example, shown at 4102 in FIG. 92A or blocks 4040,4042 or 4004 in FIG. 91. In the case of FIG. 92B, block 4150 is shownhaving four side edges 4152, 4154, 4156 and 4158 which may becorresponding to horizontal lines 4104 and vertical lines 4106. Withinthe block 4150 as bounded by edges 4152, 4154, 4156 and 4158 aconnection area 4162 is present for terminal points 4166 of anelectronic circuit 4168 to connect to terminals (not shown) of otherelectronic circuits or die I/O pads. The circuit 4168 is connected toterminal points 4166 as by intra-block (or intra-cell) wires 4170.Additional circuits may be present in the interior (or active) area 4160of the block 4150, while additional potential terminal points are shownin the connection area 4162 as by dots. The interior active area 4160 isseparated from the connection area 4162 as by dotted line 4164.

FIG. 93A shows a hexagonal block structure 4200 similar to hex block4028 of FIG. 91. Hex block 4200 is shown composed of triangularsub-blocks 4210a-4210bbb. Additional internal hexagonal sub-cellscomprise the hex block 4200, such as hex sub-block 4220 which iscomprised of triangular sub-blocks 4210s, 4210t, 4210u, 4210dd, 4210eeand 4210ff. Alternatively, hex block 4200 could be considered to becomposed of rows of rhomboid sub-blocks such as would be comprised oftriangle sub-blocks 4210a-4210g or by row of triangle sub-blocks4210vv-4210bbb. Also, hex block 4200 could be considered to be composedof abutting parallelogram sub-blocks (or sub-cells) one of which beingcomprised of triangular sub-blocks 4210a-4210f and another by 4210g,4210o, 4210p, 4210z, 4210aa and 4210ll. Further, hex block 4200 may becomprised of larger triangular sub-blocks, such as that comprisingtriangular sub-blocks 4210x-4210z and 4210jj. Thus, it is shown that hexblocks may be formed by triangle, rhomboid, parallelogram and hexsub-structures; also that parallelogram, rhomboid, hex and triangularblocks may be formed by triangular sub-blocks. Within the hex structure,the lines separating respective sub-blocks intersect at the angles θ, φand Ω as shown. Within a preferred embodiment of this invention, theintersection angles θ, φ and Ω are 60 degrees.

FIG. 93B shows an exemplar triangular block or sub-block generallydesignated by the number 4250. Block 4250 is bounded by three side edges4252, 4254 and 4256 with an interior active area 4260 surrounded by aperipheral connection area 4262, the two areas being separated as bydotted line 4264. An electronic circuit within the dotted line 4268 isshown having electrical connection to terminal points 4266 (withpotentially other terminal points shown by dots for other possibleelectronic circuits within the active area 4260 of the triangular block4250) as by intra-block (or intra-cell) wires 4270. It should be notedthat the circuit diagram shows tradition n-p transistor notation, othertypes of electronic devices, including the tri-istor disclosed herein,are specifically contemplated as circuit elements which may be designedor fabricated in the active area (4160 or 4260) of a block (4150 or4250) as shown in FIGS. 92B or 93B respectively. Additionally, eventhough the electronic circuit area 4268 is shown in a rectangular ornear-square shape in FIGS. 92B and 93B, non-square shapes arecontemplated--as by a triangular shape for tri-ister components or thelike, or hexagonal, triangular, parallelogram, rhomboidal or diamondshapes composed of tri-istors as shown herein.

Similarly to FIG. 93A, FIG. 94 shows a near-hexagonal block 4290comprised by triangular sub-blocks 4292 and having intersection anglesθ, φ and Ω of the respective separating lines at 60 degrees. Many otherregular and irregular shapes can be composed of various sub-blockshaving 60 degree intersection angles respective edge lines.

FIG. 95A shows a block 4300 similar to the block 4100 shown in FIG. 92A.Block 4300 is shown composed of triangular sub-blocks, but unlike thesub-blocks shown in FIGS. 93A and 94 primarily in the orientation of thelines which demark each sub-block. The sub-block demarcation lines inFIG. 95A define right-triangles having demarcation line intersectionangles θ and Ω of 60 degrees and φ of 90 degrees. Triangular blocks orsub-blocks are also specifically contemplated with edge lines havingother intersection angles.

Similarly to FIGS. 92B and 93B, FIG. 95B shows an exemplar triangularblock or sub-block generally designated by the number 4350. Block 4350is bounded by three side edges 4352, 4354 and 4356 with an interioractive area 4360 surrounded by a peripheral connection area 4362, thetwo areas being separated as by dotted line 4364. An electronic circuitwithin the dotted line 4368 is shown having electrical connection toterminal points 4366 (with potentially other terminal points shown bydots for other possible electronic circuits within the active area 4360of the triangular block 4350) as by intra-block (or intra-cell) wires4370. It should be noted that the circuit diagram shows tradition n-ptransistor notation, other types of electronic devices, including thetri-istor disclosed herein, are specifically contemplated as circuitelements which may be designed or fabricated in the active area (4160,4260 or 4360) of a block (4150, 4250 or 4350) as shown in FIGS. 92B, 93Bor 95B respectively. Additionally, even though the electronic circuitarea 4368 is shown in a rectangular or near-square shape in FIGS. 92B,93B and 95B, non-square shapes are contemplated--as by a triangularshape for tri-istor components or the like, or hexagonal, triangular,parallelogram, rhomboidal or diamond shapes composed of tri-istors asshown herein.

FIG. 96A shows a block structure 4620 composed of parallelogramsub-block 4602 (specifically 4602a-4602pp) of a similarity to the blocks4100, 4200, 4290 and 4300 shown in FIGS. 92A, 93A, 94 and 95A,respectively. And, similarly to FIGS. 92B, 93B and 95B, FIG. 96B showsan exemplar parallelogram block or sub-block generally designated by thenumber 4650. Block 4650 is bounded by four side edges 4652, 4654, 4656and 4658 with an interior active area 4660 surrounded by a peripheralconnection area 4662, the two areas being separated as by dotted line4664. An electronic circuit within the dotted line 4668 is shown havingelectrical connection to terminal points 4666 (with potentially otherterminal points shown by dots for other possible electronic circuitswithin the active area 4660 of the block 4650) as by intra-block (orintra-cell) wires 4670, as similarly shown and described in previouslydescribed FIGS. 92B, 93B and 95B. Herein contemplated is the specialcase parallelogram with shortened sides 4654 and 4658 forming a diamondstructured block.

FIG. 97A shows a block structure 4620' (4620 prime) composed ofrhomboidal blocks 4602', of a similarity to the blocks 4100, 4200, 4290,4300 and 4620 shown in FIGS. 92A, 93A, 94, 95A and 96A, respectively.And, similarly especially to FIG. 96B, wherein prime numerals representlike structures having non-prime similar numbers, FIG. 97B shows adetailed schematic of an electronic circuit for the block 4650' whichcould represent any one of sub-blocks 4602' of FIG. 97A.

Floorplanning

A suitable floorplanning method for such non-square die is disclosed inapplication Ser. No. 07/958,208, filed Oct. 7, 1992, by Michael D.Rostoker, entitled VARIABLE DIE SHAPE FLOORPLANNING, which isincorporated herein by reference. The floorplanning technique disclosedtherein may also be useful for increasing the available I/O area on adie vis-a-vis the active element area, thus increasing thedie-topology-efficiency. An example of a hierarchical floorplanner whichoperates at all levels of hierarchy is taught in U.S. Pat. No.4,918,614, issued Apr. 17, 1990, to Modarres et. al. (previously noted).

A method of making integrated circuits may include a floorplanningprocess comprising the steps of:

a) estimating the area required for the desired functions to beperformed by the integrated circuit;

b) estimating the area for interconnection of functions (routing);

c) estimating the area required for I/O (e.g., for bond pads);

d) calculating the ratio of function area to I/O area;

e) selecting a die shape based on the ratio; and,

f) laying out the functions and I/O on the die (floorplanning).

The last step invloves floorplanning, and also involves placement androuting optimization. A novel method for placement (which may also beused for floorplanning referred to in step (f) above) is describedbelow.

Floorplanning And Placement Optimization

Currently available computer aided design methods may not be optimum forlaying out hexagonal shaped cells on a semiconductor wafer or substrate.One aspect of the present invention is a method for optimally placinghexagonal shaped cells on the available area of a wafer. However, theplacement algorithm described herein is not limited to hexagonal shapedcells. The placement, floorplanning, and routing algorithms describedhere are applicable to rectangular cells, and other shapes of cells. Inaddition, where three layers of metal are available for routing and therouting directions are angularly offset from each other by 60 degrees, aplacement method that approaches placement in the manner describedherein is more effective at minimizing total wire length because itprovides several degrees of freedom in the same directions that routingis available. However, the disclosed algorithm is applicable to avariety of routing approaches, including rectilinear routing,multi-layer routing employing any arbitrary angular displacement betweenthe available directions, and others.

In the past, a designer would typically place large megafunction blocksin the available area of a die, and attempt would be made to see if sucha placement could be satisfactorily routed. Typically, this was doneseveral times for different placements of the megafunction blocks, andthe best result chosen. There was no assurance that any one of thelayouts determined by this partial trial-and-error approach was the bestpossible solution. The algorithm described herein allows a designer todetermine the optimum placement/floorplan from the start, because it isnot necessary to start with any blocks placed by trial-and-error. Thealgorithm is capable of determining the placement for every cell andmegafunction block on a die.

The placement method and algorithm described herein may be utilized fordesign functions commonly referred to as floorplanning, as well astraditional placement. As will be explained more fully below, theplacement of relatively large megacells is accomodated by thisalgorithm. When lower hierarchy levels are reached, megacells willbecome frozen in a particular location on the available real estate, andthe algorithm will continue to process smaller and smaller areas todetermine the placement of smaller cells. This algorithm providesdynamic floorplanning optimization.

The placement of hexagonal shaped cells may typically involve anavailable area on a chip that is non-rectangular. For example, FIG. 29shows a non-rectangular area 600 remaining on a chip after other cellsor circuits have been laid out. It is desirable to determine the mostefficient placement for hexagonal cells constructed in accordance withthe present invention. The placement problem may be addressed by usingthe placement algorithm algorithm described herein. One aspect of theplacement problem is the desire to place cells in the available region600 such that the total wire length of the metal interconnect is theminimum necessary to implement the circuit. This problem may beaddressed as involving a hypergraph "H" which is an ordered pair of twosets consisting of the set of cells to be placed on the chip, and theset of nets defining the points that must be interconnected.

H=(set of cells, set of nets).

It is desirable to minimize the total wire length of the interconnectnecessary to complete the connections between the cells in the setindicated by the set of nets. This may be stated mathematically as:

minimize total wire length=Σ_(nets) netlength!

A dynamic hierarchical placement algorithm is preferred. In thisdiscussion, "dynamic" means that cells are not fixed in any particularregion during the process of optimization. As the placement algorithmproceeds to lower levels subdividing the area under consideration, itshould be possible to move a cell from a subdivided area in one area toanother subdivided area in a completely different area if it improvesthe solution, instead of only considerating the subareas that resultfrom the subdivision of a given area. This helps avoid the phenomenum ofa local minimum, for example, in a function such as one where the totalwirelength is being minimized. This also helps to avoid a local maximum,for example, in a function where the optimization algorithm isattempting to maximize something, such as where it is maximizing anaffinity based optimization function. Thus, whether there is a potentialproblem with a local minimum, or with a local maximum, will depend uponthe type of function that is involved.

FIG. 69 depicts a flow chart for the placement algorithm disclosedherein. The steps in the algorithm may be explained with reference toFIGS. 29 and 30.

The first step 550 in the algorithm is to determine the number of levelsof hierarchy, which may be referred to as "R." The number of levels ofhierarchy, i.e., "R", may preferrably be computed from the followingformula:

    R=!log.sub.4 n

where "n" is the number of cells. This equation means that the logarithmof "n" to the base 4 is computed, and "R" is set equal to that value ifthe answer is an integer, or "R" is set equal to the next largestinteger greater than that value if the answer is not exactly an integer.In other words, "R" is an integer preferrably determined by alwaysrounding up. For example, if the number of cells "n" to be placed is1024, then the log of 1024 to the base four is exactly equal to 5. Inthis example, R=5. If the number of cells is 1,100, the the valuecomputed for the log of 1,100 to the base 4 will be a number slightlygreater than 5. This value is then rounded up to the next interger, soin this case R=6. This step is shown as step 550 in FIG. 69. When "R" iscomputed in this manner, the algorithm will proceed through levels ofhierarchy so that at the last level (i=1) each area under consideration(in this preferred embodiment, the areas are hexagonal shaped) willcontain not more than one cell. As will be explained below, other valuesof "R" may be used, and that will determine approximately how many cellswill be assigned to an area at the last level of the hierarchy.

In this algorithm, the region 600 shown in FIG. 29 is partitioned intosmaller and smaller hexagonal shaped areas. It is important to note thatthe cells do not necessarily need to be hexagonal; the hexagonal shapedareas are used to provide the appropriate degrees of freedom because thetri-direction interconnect has the same number of degrees of freedom.Hexagonal partitioning ("HP") of the region 600 is partitioned inlevels. The hex is partitioned in levels HP^(i), where i=1,2,3,4, . . .R-1, R. This step 553 (see FIG. 69) is referred to as the "hexition"step, and will be explained more fully below. Thus, the variable "i" isset equal to "R" in step 551 to start the algorithm.

The hexition step 553 may also be referred to as building a hex tilinghierarchy. The highest level of the hierarchy (with the largest hexes)is level "R", which may be referred to symbolically as HP^(R). Thislevel is represented in FIG. 29 as the larger dotted line hex 601. Inthe first initialization step 552, all cells may be placed in the centerof the "R" level hex 601. However, alternative initialization steps maybe performed, such as a Gordian initial placement algorithm, or a Chaosinitial placement algorithm. Other suitable initial placement algorithmsare known in the art. In the algorithm, the variable "i", starting withthe hierachical level "R," is decremented by one each iteration throughthe procedure (in step 554).

ITER is a variable used to keep track of the number of iterations in theloop, and is initially set to zero in step 555 each time the loop 563(comprising steps 556, 557, 558, and 559) is entered.

In the next step 556, for a given "i" (the first time through will befor hierarchy level HP^(R-1)), an initial optimization is performed. Inthe hexition step 553, the area is partitioned into hexes 602, 603, 604,605, 606, 607, and 608, etc., that are each half the size of the hex 601used in the prior hierarchical level HP^(R). In order to deal with theassignment problem mathematically, a coordinate system is used. Anyposition in the region 600 may be defined by a unique "x" and "y"coordinate pair where "x" and "y" are orthoginal axes (e.g., "x"corresponds to the horizonal axis and "y" corresponds to the verticalaxis). For each net "Q", we compute the "X" and "Y" coordinates of "Q."The "X" coordinate of "Q" may be denoted X(Q), and the "Y" coordinatemay be denoted Y(Q). The computation of X(Q) and Y(Q) will be describedin more detail below.

For each level "i" of the heirarchy, an initial optimization isperformed on level HP^(i+1). For each net "Q", the "x" and "y"coordinates of that net "Q" are computed in step 556. The number ofelements of the set (i.e., the number of pins connected in this net) maybe denoted |Q|. The "average" of the "x" coordinates and the "average"of the "y" coordinates for a net "Q" gives a "center of gravity" for thenet. The elements of the net "Q" may be designated "c". The "x"coordinate for a net "Q" is computed as follows: ##EQU2## where the "x"coordinates are summed for each "c" where "c" is an element of net "Q".

Similarly, the "y" coordinate for a net "Q" is computed as follows:##EQU3## This gives the "x" and "y" coordinates for the net "Q", whichare denoted "X(Q)" and "Y(Q)".

For each moveable cell, we compute the new "x" and "y" coordinates forthe new position of the cell in step 557. If we denote the cell as cell"c", the new "x" coordinate of the cell "c", which may be denoted"X_(new) (c)", may be computed as follows:

where Q is the set of connections for this cell, and λ is a convergenceor stability parameter that has a preferred value ##EQU4## between 0.8and 1.2. The value of λ may be chosen empirically to have thecomputation converge. If λ were chosen as 1.0, the computation would besuch that the effect would be that the new position of the cell wouldjump to the center of gravity. A convergence factor λ between 0.5 and1.5 is less preferred, but may provide satisfactory results in someinstances. The "best" value of λ is believed to be design dependent. Forexample, it may depend upon the relative number of connections that haveto be made. In many instances, suitable values for λ will be within therange of 0.5 to 1.0. Values less than 0.5 will converge slowly.

The last factor in the above equation is a weighting factor. In effect,we divide by the number of pins to avoid hot spots.

Similarly, the new "y" coordinate "Y_(new) (c)" of the cell may becomputed as follows: ##EQU5##

These computations should be repeated a number of iterations until theprocess reaches stabilization. The number of iterations ("MAX") may beselected empirically. In practice, ten to twenty iterations give goodresults, and ten to fifteen iterations is preferred.

The variable or counter "ITER" is incremented in step 558 each timethrough the loop 563. In step 559, the algorithm then checks todetermine whether the maximum number of desired iterations of the loop563 have been performed. The variable "MAX" is set equal to the maximumnumber of desired iterations. Preferred values for "MAX" are in a rangebetween 10 to 20. Additional iterations may be performed, but adiminishing rate of return is encountered. In step 559, "ITER" iscompared with "MAX" to determine whether "ITER" is less than "MAX". Ifso, the flow loops back to step 556. When the desired number ofiterations have been performed sufficient to allow the calculations toconverge to a result, (at which point "ITER" is not less than "MAX"),the flow proceeds to step 560.

Alternatively, the method could stop at step 559 if the differencebetween two consecutive values of total wire length are less than agiven small value ε. This may be expressed mathematically as follows:

|total wire length_(ITER) -total wire length_(ITER-1) |<ε

After the new coordinates "X_(new) (c)" and "Y_(new) (c)" have beencomputed after several iterations of step 557, an assignment algorithmis performed. In step 560, the "affinity" (which is detailed below) ofeach cell is computed for each hex to determine where the cell wouldprefer to be. This involves computation of the affinity of a cell forthe center 610 of the hex 602, the affinity of the cell for the center611 of the hex 604, the affinity of the cell for the center 612 of thehex 603, and so forth for each hex 605, 606, 607 and 608. In thismethod, an attempt is made to assign each cell to the hex with availablespace as to which it has the highest affinity. Each hex has a certaincapacity or area available for the placement of cells. In someinstances, all of the cells that have a maximum affinity for aparticular hex will not fit within the area available in the hex. Thecapacity of the hex is computed, and if a hex reaches its capacity,cells will then be moved or assigned to an adjacent hex as to which thecell has the next highest affinity. The assignment algorithm can beiterated a number of times to try to minimize the total interconnectlength. Alternatively, the assignment algorithm can be iterated a numberof times to try to maximize the total computed affinity value determinedby adding together the affinity value computed for each cell.

In the assignment algorithm, the affinity of a cell is computed relativeto the seven next level hexagons for level HP^(i). This step may bedescribed by referring to FIG. 30. In this illustration, the seven nextlevel hexes are hex 602, hex 603, hex 604, hex 605, hex 606, hex 607 andhex 608. The center "a" of the hex 601 at the previous hierarchicallevel "i+1" is also the center of the next hierarchical level hex 602(for the current hierarchical level "i"), and is identified by referencenumeral 610. The center 611 of hex 604 for this hierarchical level "i"may be referred to as N^(i) ₃ (a). The center 612 of hex 603 may bereferred to as N^(i) ₁ (a). Similarly, the center 613 of hex 607 may bereferred to as N^(i) ₂ (a). This same nomenclature is continued throughN^(i) ₆ (a) as the designation of the center of the last next level hex605. The affinity of cell "c" to the seven next level hexagons may bedenoted "aff(c,b)." If "b" is an element of the set of these sevenpossible locations, the affinity of cell "c" to each of the seven nextlevel hexagons may be expressed as:

    aff(c,b)=(X.sub.new (c)-X(a))*(X(b)-X(a))+(Y.sub.new (c)-Y(a))*(Y(b)-Y(a))

where X_(new) (c) and Y_(new) (c) are computed as set forth above, and"b" is an element of the set: {a, N^(i) ₁ (a), N^(i) ₂ (a), N^(i) ₃ (a),N^(i) ₄ (a), N^(i) ₅ (a), N^(i) ₆ (a)}. Thus, the above computation isperformed seven times for each cell during an iteration. Of course, X(a)is the "x" coordinate of the center 610 of the center hex 602, and Y(a)is the "y" coordinate of the center 610 of the center hex 602.Alternatively, other assignment algorithms may be used.

N^(i) ₁ (a) refers to the "neighbor" "N". For each cell c, and for eachof the seven "neighbors" on the currect hierachy HP^(i), the affinityaff(c,b) is computed in step 560 for the hex in which c is in the centeron the prior hierachial level HP^(i+1).

As described above, an attempt is made to assign each cell to a hex withavailable space as to which the cell has the greatest computed affinity.However, each hex has a certain capacity or area available for theplacement of cells. In some instances, all of the cells that have amaximum affinity for a particular hex, for example hex 603, will not fitwithin the area available in the hex 603. The capacity of each hex iscomputed, and if a hex reaches its capacity, cells will then be moved orassigned to an adjacent hex as to which the cell has the next highestaffinity.

The total length of interconnect wire may be computed at the end of eachiteration of the assignment algorithm, and the process is repeated untilthe total length of interconnect wire does not become shorter ascompared to the total length of interconnect wire computed for the prioriteration. Alternatively, the assignment algorithm can be iterated anumber of times to try to maximize the total computed affinity valuedetermined by adding together the affinity value "aff(c,b)" computed foreach cell.

After the iterations of the assignment algorithm have been completed,"i" is decremented and the procedure proceeds to the next level HP^(i-1)of the heirarchy. Thereafter, each time through the loop 564, "i" isdecremented in step 554 and the procedure proceeds to the next levelHP^(R-2) of the heirarchy and so forth. The process is repeated for each"i" until i=0. The last level where i=0 may be referred to as level HP⁰.By the time the last level HP⁰ is reached, each hex preferrably willcontain not more than a single cell, or a "zero," i.e., the cell isempty. Alternatively, the last level HP⁰ may be chosen (that is, thevalue of "R" may be selected) so that each hex contains not more thanabout two or three cells. Useful results may be achieved if "R" isselected so that the last level HP⁰ results in each hex containing notmore than four cells. The last level HP⁰ will have the smallest hexes.When step 561 is reached on the last hierarchical level, "i" will equalone, and the flow proceeds to step 562.

In the above discussion with reference to step 557, for each "moveable"cell, the new "x" and "y" coordinates are computed. In the beginning,virtually all cells are "moveable" cells. As the algorithm proceeds tolower levels in the hierarchy, the size of the hexes 602 become smaller.When the size of the hexes 602 becomes so small that a particular cellis then "bigger" than the size of the hexes at that level, the cellbecomes frozen and is no longer moveable. In this context, "bigger"means that any dimension of the cell is bigger than the size of the hex.For example, the cell overlaps the hex and cannot be made to fitcompletely within the area of the hex. In this way, even large megacellscan be placed with this algorithm, because the large megacells willbecome frozen when the hex size gets to be too small, and the remainderof the cells will be optimally placed relative to the megacell. However,in the present algorithm, unlike the prior art, the megacell will be inan optimum location relative to the remainder of the components. Themegacell will not be moved as the algorithm proceeds to lower levels,but should be optimally located so that the remaining cells can beoptimally laid out in an effective floorplan.

Additional disclosure relating to CAD design methods is provided in U.S.Pat. No. 5,222,030, to Carlos Dangelo, et al., the entirety of which isincorporated herein by reference; application Ser. No. 08/229,826, filedApr. 19, 1994, by Michael D. Rostoker, et al., entitled INTEGRATEDCIRCUIT PHYSICAL DESIGN AUTOMATION SYSTEM UTILIZING OPTIMIZATION PROCESSDECOMPOSITION AND PARALLEL PROCESSING, the entirety of which isincorporated herein by reference; and application Ser. No. 08/016,864,filed Feb. 10, 1993, by Michael D. Rostoker, entitled FLOORPLANNINGTECHNIQUE USING MULTI-PARTITIONING, the entirety of which isincorporated herein by reference.

Routing

The placement phase involves floor planning and completion of theplacement algorithm. On completion of the placement phase of the design,to make the layout functional, all of the interconnections need to beestablished. This process of establishing the interconnections is calledrouting. The above placement algorithm provides first order solution tothe routing problem, because the cells should be placed in locations tomake it easier to successfully route the interconnections. For somechips, it may be sufficient to minimize the total wire length. For highperformance chips, it may be desirable to minimize the length of thelongest wire in order to minimize the delay in such wire to maximizeperformance. Routing algorithms may need to consider parameters such asthe number of terminals per net, width of nets, different types of nets,restrictions on vias, shape of any routing boundaries, and the number ofavailable routing layers.

A circuit consists of a set of modules (or cells) and a set of nets.Each net specifies a subset of points on the boundary of modules, calledterminals. The region that is not occupied by modules can be used forrouting. In addition, over-the-cell routing may be available. Thesolution of a routing problem may consist of connections of terminals ofnets by a set of curves (which define wires), where two end points ofeach curve belong to the same net. In a k-layer routing problem, a curveor a piece of a curve may be assigned to any of the k layers. Vias areassigned at points where a curve changes layers, (assuming no twodistinct curves intersect in the same layer. In one embodiment of thepresent invention, three layers of routing are available (i.e., k=3).

A routing algorithm suitable for implementation as a computer aideddesign tool is desirable to assist in designing a semiconductor deviceaccording to the present invention. A routing algorithm that gives goodresults with three layers of metal is desirable.

Conventional routing methods often result in unbalanced routing layers.For example, FIG. 31 and FIG. 32 graphically illustrate routing densityfor the first metal layer and for the second metal layer, respectively,of an example of a circuit. The density of routing in the first metallayer M1 shown in FIG. 31 is much greater than the density of routing inthe second metal layer M2 shown in FIG. 32. In this example, the firstmetal layer M1 associated with FIG. 31 was used for routing in thevertical direction in a rectangular routing design. The second metallayer M2, the density of which is shown in FIG. 32, was used for routingin the horizontal direction. Any attempt to balance the routing betweenthese two layers of metal would require more interlayer interconnect(i.e., using vias), and it is not possible to punch through the firstmetal layer and form a via from the substrate to the second metal layerif a wire is present in the first metal layer at the desired location ofthe via.

FIG. 33 and FIG. 34 depict the routing density for another example of atwo metal layer design having unbalanced routing. FIG. 33 graphicallyillustrates the density of routing in the first metal layer in arectangular two metal layer design. FIG. 34 graphically illustrates thedensity of routing in the second metal layer in the same rectangular twometal layer design.

The balance of interconnection layers is important. First, an imbalancethat results in very dense routing in the first layer of metal may causeso much congestion that it will not be possible to get a wire through,for example to another metal layer, without resorting to an undesirableoption such as increasing the size of the chip. Second, photolithographyworks better when it is performed in a balanced chemical environment. Itis desirable to perform a uniform chemical etching of the substrate. Ifone part of the circuit has a great number or amount of wires ascompared to another part of the circuit which has only a few wires, thearea with relatively few wires may be etched at a rate different fromdenser areas of the circuitry. It is sometimes necessary to place unusedmetal that has no functional purpose in the circuit, referred to asbogus metal, in the area with relatively few wires in order to balancethe chemicals. This is sometimes referred to as the lonely wire problem.

Polydirectional non-orthoginal three layer routing of non-resin circuitstructures according to the present invention can balance the density ofrouting in the layers. As used herein, "polydirectional non-orthoginalthree layer routing" refers to interconnection using three layers ofmetal where the direction of routing implemented in each layer of metalis angularly displaced from the direction of routing employed in theother metal layers by an angle less than ninety degrees, but excludingangular displacements of forty-five degrees. "Non-resin circuitstructures" is defined to include semiconductor substrates, but thedefinition excludes circuit boards.

A routing algorithm determines the selection of one of several possibleroutes which may be used to connect two points in a circuit. Each cellin the design may have one or more pins that must be electricallyconnected to pins on other cells. Interconnection is typicallyaccomplished by metal wires constructed in one or more of the metalinterconnect layers. If pins that are to be interconnected are termednodes, then the problem may be expressed as starting with a given set ofnodes (or nets), and a given set of interconnections between the nodes(or nets), what is an optimum routing to accomplish the desiredinterconnections. In the following description, nodes are sometimes alsoreferred to as points.

In the past, routing problems have involved two layers, and two possiblerouting directions, (i.e., vertical or horizontal). Now, the problemmust be addressed in the context of three routing layers, and threeavailable routing directions. It is desirable to have a routingalgorithm capable of solving tri-directional routing problems in a moreoptimum fashion.

A routing algorithm for use in connection with tri-directional routingin accordance with one aspect of the present invention is depicted inthe flow chart of FIG. 70. The first step 575 in the procedure is toread into the system the netlist providing the set of nodes to beconnected. A chip and cell library is read in as well in step 575.

Some nets or nodes may be multi-pin nets, (which are sometimes referredto as multi-terminal nets). That is, in some nets more than two pinsmust be interconnected together. The multi-pin nets are first reduced topairs of pins. The routing algorithm is much more manageable if the netlist is first redefined as a set of pairs of pins. Step 576 in FIG. 70represents the step in which this is performed. Step 576 is shown inmore detail in FIG. 71.

In the illustrated routing method, the set of nets is input in step 588.The first time through, a net is initially selected in step 589. Insubsequent iterations, the next net will be selected, and so forth,until every net has been processed.

The algorithm looks to see if the net selected is a multi-pin net instep 590. If it is not, nothing needs to be done at this point, and theprocedure loops back to step 589, (and the next net is selected). If anet is a multi-pin net, the procedure determines a minimum spanning treein step 591 (shown in more detail in FIG. 72). After the minimumspanning net has been determined for this net, the procedure checks todetermine if all nets have been processed in step 592 shown in FIG. 71.If not, the procedure loops back to step 589. If all nets have beenprocessed, an output set of net pairs is returned in step 593 and flowproceeds to step 577 in FIG. 70.

Step 591 in FIG. 71 is depicted in detail in FIG. 72. In step 565, amulti-pin set of points is selected. A counter "i" is set equal to zeroin step 566. The method then includes the step of calculating thedistance between every possible pair of points (or pins). These pointsare sometimes referred to as demand points.

In step 568, the shortest remaining distance between remainingunconnected points is selected. This is examined to make sure it doesnot form a closed path, i.e., all of the connections form a polygon thatcloses in some area. If it does, that segment is eliminated as apossible pair connection in step 570, and flow loops back to step 568.

If the selected connection pair does not form a closed path, flowproceeds to step 571 and the pair is stored. In step 572, the counter"i" is incremented. The method includes the step of checking todetermine whether "i"=K-1, that is, have all of the points beenconnected in pairs. If not, the flow loops back to step 568. The loop isrepeated until all points are sorted into connected pairs, and flowproceeds to step 574. While this approach does not generate anyadditional points, (typically called "Steiner points"), it will work ina three directional routing system. In addition, in a three directionrouting system, the routing distances tend to be shorter anyway due tothe additional degrees of freedom, so there is not as much pressure tofurther optimize the pairs. Of course, certain "L" points may be createdwhere two points must be connected by routing in two or more directions.In other words, a connection cannot be made in a straight line with theavailable routing directions.

Multi-pin nets have in the past been reduced to pairs in a rectilinearrouting system using Steiner tree algorithms. As shown in FIG. 71,Steiner tree algorithms optionally may be used to further optimize theconnection pairs in the alternative optional step 594, if desired.Steiner tree algorithms are discussed in N. Sherwani et al., Routing InThe Third Dimension, at 81-86 (1995) (and references cited therein)

A Steiner Minimum Tree (SMT) problem can be defined as follows: Given anedge weighted graph G=(V,E) and a subset D.OR right.V, select a subsetV'.OR right.V, such that D.OR right.V' and V' induces a tree of minimumcost over all such trees. The set D is referred to as the set of demandpoints and the set V'-D is referred to as Steiner points. It is easy tosee that if D=V, then SMT is equivalent to the corresponding minumumspanning tree for this net. On the other hand, if |D|=2 then SMT isequivalent to the single pair shortest path ("SPSP"). Unlike MST andSPSP, SMT and many of its variants are NP-complete. In view of theNP-completeness of the problem, several heuristic algorithms have beendeveloped.

Steiner trees arise in VLSI physical design in routing of multi-terminalnets. Consider the problem of interconnecting two points in a planeusing the shortest path. This problem is similar to the routing problemof a two terminal net. If the net has more than two terminals then theproblem is to interconnect all the terminals using minimum amount ofwire, which corresponds to the minimization of the total cost of edgesin the Steiner tree. The global and detailed routing of multi-terminalnets is an important problem in the layout of VLSI circuits. Thisproblem has traditionally been viewed as a Steiner tree problem. Due totheir important applications, Steiner trees have been a subject ofintensive research.

An underlying grid graph in a rectilinear routing system is the graphdefined by the intersections of the horizontal and vertical lines drawnthrough the demand points. The problem is then to connect terminals of anet using the edges of the underlying grid graph. Steiner tree problemsare mostly defined in the Cartesian plan, and edges are typicallyrestricted to be rectilinear. A Steiner tree whose edges are constrainedto rectilinear shapes is called a Rectilinear Steiner Tree (RST). ARectilinear Steiner Minimum Tree (RSMT) is an RST with minimum costamong all RSTs.

Suitable Steiner tree algorithms for three directional routing may beused in alternative step 594. Steiner tree algorithms are disclosed inapplication Ser. No. 08/131,770, filed Oct. 4, 1993, by Scepanovic, etal., entitled TOWARDS OPTIMAL STEINER TREE ROUTING IN THE PRESENCE OFRECTILINEAR OBSTACLES, the entiriety of which is incorporated byreference. Algorithms are further disclosed by P. Chaudhuri, RoutingMultilayer Boards On Steiner Metric, 1980 IEEE International SymposiumOn Circuits And Systems Proceedings, at 961-964 (1980), the entiriety ofwhich is incorporated by reference, and M. Sarrafzadeh, et al.,Hierarchical Steiner tree Construction in Uniform Orientations, IEEETransactions On Computer-Aided Design, Vol. II, No. 9 (September 1992),the entiriety of which is incorporated by reference.

Referring to FIG. 70, the routing algorithm continues with aninitialization step 577 after the data set has been reduced to a set ofpairs. In step 578, the next pair is selected. The possible routes areexamined using Lee's algorithm to find a path between the selected pair.The algorithm has an exploration phase and backtrack phase known tothose skilled in the art.

A first source point which must be connected to a second demand point isassigned a certain value, or amount of capital, that the first point may"bid" on each segment of a possible connection routes to the secondpoint. Where a path requires metal in more than one layer, each portionof the path that lies in the same layer is a segment. If severalpossible routes are available, the first point divides the value it hasto bid equally among the available segments of the available routes. Athird point may, for example, only have one possible route available forconnection but it may be a route that conflicts with one or more of thepossible routes available to the first point. In other words, if a wireis run from the third point to its desired connection point along theone available route, then it will occupy the same real estate that is inthe path of one of the possible routes between the first point and thesecond point. In this example, the third point bids its entire value onthis one route. Because the value bid on the single possible routerequired for the connection of the third point is greater than the valuebid on the conflicting route between the first point and the secondpoint, the third point "out bids" the first point and wins theconflicting real estate. The routing algorithm assigns that route to thethird point. An example is shown in FIG. 35.

A first point 620 shown in FIG. 35 must be connected to a second point621. More than one possible route is available. A first possible route624 and a second possible route 625 are shown as dotted lines. Otherpossible routes may exist, but only two are shown for purposes ofdiscussion in order to simplify this example. A third point 622 must beconnected to a fourth point 623. In this example, only one possibleroute 626 is available. If the wire 626 is put down as shown, then itwill occupy a portion 627 of the path of the first possible route 624between the first point 620 and the second point 621. If the route 626is used to connect the third point 622 and the fourth point 623, thenthe route 624 cannont be used to connect the first point 620 and thesecond point 621, because a short circuit would result.

Although bidding is actually determined by segments, the followingexample will discuss bidding in a simplified manner. If the first point620 and the second point 621 have a value of "100" to bid on availableroutes, a value of "50" would be bid on the first route 624 and a valueof "50" would be bid on the second route 625. The third point 622 andthe fourth point 623 similarly have a value of "100" to bid on availableroutes. A value of "100" would be bid on the only available route 626.In view of the fact that the third and fourth points 622 and 623 bid"100" on the route 626 and the first and second points 620 and 621 bid avalue of "50" on the route 624, the third and fourth points 622 and 623will win the auction and be assigned the route 626 by the routingalgorithm.

In step 581, the winning bids are determined. Where a path has a winningbid, and the segments add together to form a connection path between thetwo points, the path is stored in step 583 and the method proceeds toprocess all of the pins or pairs.

The auction may be repeated a number of iterations. If all pairs are notrouted when step 585 is reached, the capital available to be bid onavailable connections will be increased for those pairs that wereblocked, and the procedure repeats by looping back to step 587.

The preferred algorithm is shown in FIG. 70. However, alternatively, analgorithm could loop back from step 587 to step 578 and attempt to holdan auction between remaining blocked pairs. In the example illustratedin FIG. 35, the route 626 is assigned to the third and fourth points 622and 623 in the first iteration. When the second iteration is performed,the route 626 has already been assigned. Thus, in the second iteration,the route 624 in not available as a possible connection between thefirst point 620 and the second point 621. In the second iteration, thereis now only one possible route 625 available for connection between thefirst point 620 and the second point 621. In the second iteration of theauction, the first point 620 and the second point 621 have a value of"100" to bid on possible routes. The entire value "100" is bid on theonly available route 625. In this iteration, the first and second points620 and 621 out bid all other competitors (not shown) and are assignedroute 625.

The assignment algorithm may refine the bidding process to betteroptimize routing. In the first round of bidding, a constraint may beimposed upon the bidding to restrict bidding to choices that have a costin terms of chip area that is less than or equal to a predeterminedvalue. In later iterations, if a solution is not found, the constraintsmay be relaxed to expand the possible choices to allow bidding uponconnections that are longer. This assignment algorithm should settle outwith optimum routing locations for interconnection.

Alternatively, greedy and maze routing techniques may be used in arouting algorithm to complete the routing. Additional disclosure of anauction algorithm is shown in D. Bertsekas, Auction Algorithms ForNetwork Flow Problems: A Tutorial Introduction, ComputationalOptimization And Applications, at 7-66 (1992), the entiriety of which isincorporated herein by reference.

In an alternative embodiment, four layers on metal may be used. Analternative routing algorithm for four layers of metal is described inE. Katsadas et al., "A Multi-Layer Router Utilizing Over-Cell Areas,"Proceedings of 27th Design Automation Conference, at 704-708 (1990) andN. Sherwani et al., Routing In The Third Dimension, at 15 (1995). Thisexample algorithm completes routing in two steps. A selected group ofnets are routed in the between-cell areas using existing channel routingalgorithms and the first two routing layers. Then the remaining nets arerouted over the entire layout area, between-cell and over-the-cellareas, using a two-dimensional router and the next two routing layers.

Alternatively, two and one-half layers of interconnect may be used forrouting. Preferrably, the layers of interconnect are metal, but thefirst half layer may be polysilicon, polysilicide, or metal. Half layermetal is fabricated as the first metal layer. This first layer isreferred to as a half layer because it is thinner than normal. Such thinmetal layers are cheaper to produce, but are limited in the length thatsuch wires may be fabricated without paying significant performancepenalties. Thus, the first half layer of metal is used for localinterconnect. This relieves congestion in the other layers of metal.Tri-directional routing is preferrably used.

Another alternative embodiment uses three and one-half layers of metal.Yet another embodiment uses four and one-half layers of metal. Four andone-half layers of metal should avoid all routability problems for allbut the most dense and complicated circuit designs.

Multiple layers of metal (two and one half layers or more) preferrablyare laid out using tri-directional routing as described herein. Althoughsuch routing arraingements may be advantageously used in connection witha hexagonal cell layout on a semiconductor substrate, thetri-directional routing may also be effectively used in connection withrectangular cells. Multiple metal layer tri-directional routing is notlimited to a hexagonal cell layout.

Suitable process technology for producing a very large scale integratedcircuit in accordance with the present invention is disclosed in U.S.Pat. No. 5,358,886, the entire disclosure of which is incorporatedherein by reference; and in application Ser. No. 08/086,217, filed Jul.1, 1993, the entire disclosure of which is incorporated herein byreference. For example, 0.35-micron CMOS ASIC technology may providesatisfactory results in practice. Additional disclosure of a flip chipdie-to-die configuration is disclosed in application Ser. No.07/975,185, filed Nov. 12, 1992, by Michael D. Rostoker, the entiredisclosure of which is incorporated herein by reference.

Triangular Semiconductor AND Gate

A semiconductor gate device for a microelectronic integrated circuit isdesignated by the reference numeral 30 and illustrated in FIG. 36. Thedevice 30, in its basic form, provides a logical AND function, but canbe adapted to provide a logical NAND, OR, NOR, or other logical functionas will be described below.

The gate device 30 is formed on a substrate 32, and has a triangularperiphery 34 including first to third edges 34-1, 34-2 and 34-3, andfirst to third vertices 34-4, 34-5 and 34-6 respectively in theillustrated arrangement. A triangular semiconductor active area 36 isformed within the periphery 34, and an inactive area 38 is definedbetween the active area 36 and the periphery 34.

The device 30 comprises a first electrically conductive electrode orterminal 40 which functions as a Field-Effect-Transistor (FET) sourceterminal, and a second electrode or terminal 42 which functions as anFET drain terminal. The terminals 40 and 42 are formed in the activearea 36 adjacent to the first and second vertices 34-4 and 34-5respectively. Although only one each of the terminals 40 and 42 isillustrated in the drawing, it is within the scope of the invention toprovide two or more each of the terminals 40 and 42.

The device 30 further comprises first, second and third gates 48, 50 and52 which are formed between the first and second terminals 40 and 42respectively as illustrated. The gates 48, 50 and 52 are preferablyinsulated gates, each including a layer of insulating oxide with a layerof conductive material (metal or doped polysilicon) formed over theoxide in a Metal-Oxide-Semiconductor (MOS) configuration.

First to third gate electrodes or terminals 54, 56 and 58 are formed inthe inactive area 38 adjacent to the triangular edge 34-1, and areelectrically connected to the gates 48, 50 and 52 respectively. It willbe noted that the locations of the gate terminals 54, 56 and 58 areexemplary, and that the gate terminals can be located at differentpoints in the device in accordance with the requirements of a particulardesign or application.

In order to provide effective source-drain electrical isolation, theopposite end portions of each of the gates 48, 50 and 52 extend into theinactive area 38. The upper end of the gate 56 has the shape of as asolid quadrilateral which extends into the inactive area 38 as indicatedat 50a. This is for the purpose of avoiding manufacturing problems whichcould result if the upper end of the gate 50 extended through the uppervertex of the triangular active area 36. Other layout schemes could beused to achieve this purpose of making the design immune tomanufacturing tolerances.

The device 30 shown in FIG. 36 in its most basic form provides a logicalAND function. Each gate 48, 50 and 52 controls the electricalconductivity of a respective underlying portion of an FET channelbetween the terminals 40 and 42 such that each gate 48, 50 and 52 canindependently inhibit conduction through the channel. Signals must beapplied to all of the gates 54, 56 and 58 which cause the underlyingportions of the channel to become enhanced in order to enable conductionthrough the channel. This is an "all" or "AND" configuration.

An AND gate 60 based on the device 30 is illustrated in FIG. 37. Thedevice 30 is shown in simplified form for clarity of illustration, withonly the triangular periphery 34 and terminals 40, 42, 54, 56 and 58included in the drawing. Input signals A, B and C are applied to thegate terminals 54, 56 and 58 respectively, and an output signal OUT istaken at the source terminal 40.

In the AND gate 60 of FIG. 37, the active area 36 of the device 30 isP-type to provide NMOS FET operation. The drain terminal 42 is connectedto an electrical potential V_(DD) which is more positive than ground.The terminal 40 is connected to ground through a pull-down resistor 62.

A logically high signal will be assumed to be substantially equal toV_(DD), and a logically low signal will be assumed to be substantiallyequal to ground. With any logically low input signal A, B or C appliedto the gate terminal 54, 56 or 58 respectively, the device 30 will beturned off and the resistor 62 will pull the output low (to ground).

Since the device 30 provides NMOS operation in the configuration of FIG.37, positive inputs to all of the gate terminals 54, 56 and 58 willestablish a conductive channel between the terminals 40 and 42. Theentire channel will be enhanced, thereby connecting the source terminal40 to the potential V_(DD) through the drain terminal 42 to produce alogically high output. In this manner, the AND gate 60 produces alogically high output when all of the inputs are high, and a logicallylow output when any of the inputs are low.

FIG. 38 illustrates the device 30 connected in circuit to function as aNAND gate 64. In this case also, the active area 36 of the device 30 isP-type to provide NMOS operation. The source terminal 40 is connected toground, and the drain terminal 42 is connected to V_(DD) through apull-up resistor 66. The output signal OUT appears at the drain terminal42.

When any of the inputs are low, the device 30 is turned off and theoutput will be pulled to V_(DD) by the pull-up resistor 66 to produce alogically high output. If all of the inputs are high, a conductivechannel will be established between the terminals 40 and 42 to connectthe output to ground and produce a logically low output. In this manner,the output signal OUT will be high if any of the inputs are low, and lowif all of the inputs are high to produce the NAND function.

An OR gate 70 incorporating the device 30 is illustrated in FIG. 39. Inthe OR gate configuration, the active area 36 is N-type to provide PMOSFET operation, and the drain terminal 42 is connected to ground. Thesource terminal 40 is connected to V_(DD) through a pull-up resistor 72,and the output is taken at the source terminal 40.

Due to the PMOS configuration of the device 30 in the OR gate 70, all ofthe input signals A, B or C must be logically low to establish aconductive channel between the terminals 40 and 42. This connects theoutput to ground. Thus, all low inputs will produce a low output. Whenany of the inputs is high, the device 30 is turned off, and the outputis pulled high by the pull-up resistor 72. Thus, the desired OR functionis provided.

A NOR gate 74 incorporating the device 30 is illustrated in FIG. 40, inwhich the active area 36 is N-type to provide PMOS operation. The sourceterminal 40 is connected to V_(DD), whereas the terminal 42 is connectedto ground through a pull-down resistor 76. The output is taken at theterminals 42.

All low inputs will establish a conductive channel between the terminals40 and 42, thereby connecting the output to V_(DD) and producing a highoutput. When any of the inputs are high, the device 30 is turned off andthe output is pulled to ground by the resistor 76. Thus, the NORconfiguration is provided, in which any high input produces a lowoutput, and the output is high in response to all inputs being low.

The device 30 is illustrated as having three inputs, which is ideallysuited to the triangular device shape. However, it is within the scopeof the invention to provide a gate device having one or two inputs. Adevice with one input can be used as a buffer or an inverter.

The device 30 can be configured without modification to operate as if ithad one or two, rather than three inputs. For example, if it is desiredto operate the AND gate 60 of FIG. 37 with only two inputs, the gateterminal 58 can be connected to V_(DD) and the two inputs applied to thegate terminals 54 and 56. The OR gate 70 of FIG. 39 can be adapted toprovide a two input configuration by connecting the gate terminal 58 toground and applying the two inputs to the gate terminals 54 and 56.

It is also within the scope of the invention to modify the device 30 tohave only one or two inputs by physically omitting one or two of thegates 48, 50 and 52 and respective terminals 54, 56 and 58.

FIG. 41 illustrates alternative locations for the gate terminals 54, 56and 58 in a modified device 30'. Rather than providing all of the gateterminals 54, 56 and 58 adjacent to the lower edge of the triangle, itis within the scope of the invention to provide gate terminals 54', 56'and 58' at the upper end portions of the gates 48, 50 and 52respectively.

It is also within the scope of the invention to provide a gate terminal56" adjacent to the upper vertex of the quadrilateral 50a. In general,the gate terminals can be formed at any desired location as long as theyelectrically interconnect with the gates.

An example of the device 30 as being interconnected using the hexagonalrouting arrangement of the present invention is illustrated in FIG. 42.It will be understood that the particular interconnect directions shownin the drawing are selected arbitrarily for illustrative purposes, andare not in any way limitative of the scope of the invention. In general,any of the wiring directions can be utilized to interconnect any of theelements of the device 30.

In the illustrated example, a conductor 1160 which extends in thedirection e₂ is provided for interconnecting the gate terminal 54' forthe input A. A conductor 1162 which extends in the direction e₁ isprovided for interconnecting the gate terminal 56" for the input B,whereas a conductor 1164 which extends in the direction e₃ is providedfor interconnecting the gate terminal 58' for the input C.

Conductors 1166 and 1168 which extend in the directions e₂ and e₃ areprovided for interconnecting the source terminal 40 and drain terminal42 respectively.

The conductors 1160, 1162 and 1164 are preferably provided in threeseparate wiring layers respectively. The conductors 1166 and 1168 arepreferably provided in another wiring layer or conductive plane.

FIG. 43 illustrates a microelectronic integrated circuit 1180 accordingto the present invention comprising a semiconductor substrate 1182 onwhich a plurality of the devices 30' are formed in a closely packedtriangular arrangement. Further shown are a few illustrative examples ofinterconnection of the devices using the conductors 1160, 1162, 1164,1166 and 1168 which extend in the three directions described withreference to FIG. 42.

It will be noted that six closely packed devices 30 define a hexagonalshape having a periphery 1184. This relationship can be used within thescope of the invention to provide unit cells having hexagonal shapesdefined by closely packed triangles, with internal structures similar toor different from that those which are explicitly described andillustrated. In such an arrangement, the hexagon can be considered to bethe basic building block.

It will be understood from the above description that the present gatedevice geometry and three direction interconnect arrangementsubstantially reduce the total wirelength interconnect congestion of theintegrated circuit by providing three routing directions, rather thantwo as in the prior art. The three routing directions include, relativeto a first direction, two diagonal directions that provide shorterinterconnect paths than conventional rectilinear routing.

In addition, the number of conductors that extend parallel to each otheris smaller, and the angles between conductors in different layers arelarger than in the prior art, thereby reducing parasitic capacitance andother undesirable effects that result from conventional rectilinearrouting.

FIG. 44, FIG. 45, and FIG. 46 illustrate how the device 30 can bemodified to provide a different logical function. In an AND/OR gate1200a, a third terminal 1202 is formed between the gates 50 and 52.

In the gate 1200a, the first and second terminals 40 and 42 areconnected to V_(DD) to constitute drain terminals, and the output signalOUT appears at the third terminal 1202 which functions as a sourceterminal and is connected to ground through a pull-down resistor 1204.

The gate 1200a provides the logical function (A•B)+C. As illustrated inthe equivalent circuit diagram of FIG. 45, the inputs A and B areapplied to inputs of an AND gate 1206, the output of which is applied toan input of an OR gate 1208. The input C is applied to another input ofthe OR gate 1208, whereby the output of the OR gate 1208 is (A•B)+C.

The gates 48 and 50 are both disposed between the terminals 42 and 1202,and high inputs must be applied to both respective gate terminals 54 and56 to enhance the entire portion of the channel between the terminals 42and 1202 to connect the terminal 1202 to V_(DD) via the terminal 42 andproduce a high output signal OUT.

However, only the gate 52 is disposed between the terminals 40 and 1202,such that a high signal applied to the gate terminal 58 alone issufficient to connect the terminal 1202 to V_(DD) via the terminal 40.

In this manner, the output of the gate 1200a will be logically high ifthe inputs A and B are both high, and/or the input C is logically high,and the output of the gate 1200a will be logically low if either of theinputs A and B are low, and the input C is low.

The gate 1200a is illustrated in the form of equivalent FET transistorsin FIG. 46. The functionality of an FET 1210 is provided by the secondterminal 42 and the first gate 48 as shown in FIG. 44. The functionalityof an FET 1212 is provided by the second terminal 42 and second gate 50,whereas the functionality of an FET 1214 is provided by the firstterminal 40 and the third gate 52.

Similar operation can be obtained by providing the third terminalbetween the gates 48 and 50. The principle is that by providing anoutput terminal between two of the gates and connecting the first andsecond terminals 40 and 41 to V_(DD), a high input signal applied to oneof the gates can produce a high output, whereas high input signalsapplied to the other two gates are alternatively required to produce ahigh output.

It will be noted that reversal of source and drain connections toprovide alternative logic functions is possible for all embodiments ofthe invention as described above.

Space in the present triangular AND gate device is used most efficientlyin the illustrated configuration, in which the terminals 40 and 42 aredisposed adjacent to the vertices of the triangle and the gate terminals48, 50 and 52 are disposed adjacent to the edges of the triangularperiphery 34. However, the present invention is not so limited, and itis possible to locate the terminals adjacent to the edges, and locatethe gate terminals adjacent to the vertices of the triangular periphery34. Other arrangements of the terminals, although not explicitlyillustrated, are possible within the scope of the invention.

Another modification of the present gate device is illustrated in FIG.47, and designated as 30". As described above, manufacturing problemscan be encountered if the upper end of the gate 50 extends through theupper vertex of the triangular active area 36. FIG. 47 illustrates analternative method of overcoming this problem, in which the upper vertexof the active area 36" is truncated to form a horizontal edge 36a", andthe upper portion of the gate 50 extends perpendicularly through theedge 36a".

Triangular CMOS NAND Gate Device

A semiconductor CMOS gate device for a microelectronic integratedcircuit is designated by the reference numeral 30a and illustrated inFIG. 48. The illustrated device 30a, in its basic form shown in thisexample, provides a logical NAND function, but can be adapted to providea logical AND, NOR, OR or other logical function as will be describedbelow.

Referring to FIG. 48, the gate device 30a is formed on a substrate 32,and includes a logical "ALL" element 1331 having a triangular periphery1134 including first to third edges 1134-1, 1134-2 and 1134-3, and firstto third vertices 1134-4, 1135-6 and 1135-7 respectively in theillustrated arrangement. A triangular semiconductor active area 1136 isformed within the periphery 1134, and an inactive area 1138 is definedbetween the active area 1136 and the periphery 1134.

The ALL element 1133 comprises an electrically conductive electrode orterminal 1140 which is formed in the active area 1136 adjacent to thevertex 1134-6 and functions as a Field-Effect-Transistor (FET) sourceterminal. Another electrode or terminal 1142 is formed in the activearea 1136 adjacent to the vertex 1134-5 and functions as an FET drainterminal.

The ALL element 1133 further comprises gates 1148, 1150 and 1152 thatare formed between the terminals 1140 and 1142. The gates 1148, 1150 and1152 are preferably insulated gates, each including a layer ofinsulating oxide with a layer of conductive metal formed over the oxidein a Metal-Oxide-Semiconductor (MOS) configuration.

In order to provide effective source-drain electrical isolation, theopposite end portions of each of the gates 1148, 1150 and 1152 extendinto the inactive area 1138. The lower end of the gate 1150 has theshape of a solid quadrilateral which extends into the inactive area 1138as indicated at 1150a. This is for the purpose of avoiding manufacturingproblems which could result if the lower end of the gate 1150 extendedthrough the lower vertex of the triangular active area 1136. Otherlayout schemes could be used to achieve this purpose of making thedesign immune to manufacturing tolerances.

The ALL element 1133 in its most basic form provides a logical ANDfunction. The terminal 1140 functions as a source terminal, whereas theterminal 1142 functions as a drain terminal of a field effecttransistor, with a channel being defined between the terminals 1140 and1142.

Each gate 1148, 1150 and 1152 controls the electrical conductivity of arespective underlying portion of the channel such that each gate 1148,1150 and 1152 can independently inhibit conduction through the channel.Signals must be applied to all of the gates 1148, 1150 and 1152 whichcause the underlying portions of the channel to become enhanced in orderto enable conduction through the channel. This is an "ALL" or "AND"configuration.

The device 30a further includes an "ANY" element 1233 having atriangular periphery 234 including first to third edges 1234-1, 1234-2and 1234-3, first to third vertices 1234-4, 1234-5 and 1234-6respectively in the illustrated arrangement, and an active area 1236. Aninactive area 1238 is defined between the active area 1236 and theperiphery 1234.

The ANY element 1233 comprises a central electrically conductiveelectrode or terminal 1240 which functions as a source terminal, andelectrodes or terminals 1242, 1244 and 1246 which are formed in theactive area 1236 adjacent to the vertices 1234-5, 1234-4 and 1234-6respectively.

The terminals 1242, 1244 and 1246 function as FET drain terminals, andare preferably interconnected for operation. Although one each of theterminals 1242, 1244 and 1246 are illustrated in the drawing, it iswithin the scope of the invention to provide two or more of each of theterminals 1242, 1244 and 1246.

The ANY element 1233 further comprises gates 1248, 1250 and 1252 thatare formed between the terminals 1242, 1244 and 1246 respectively andthe central terminal 1240. The gates 1248, 1250 and 1252 are preferablyinsulated gates, each including a layer of insulating oxide with a layerof conductive metal formed over the oxide in a MOS configuration.

In order to provide effective source-drain electrical isolation, theopposite end portions of each of the gates 1248, 1250 and 1252 extendinto the inactive area 1238.

The ANY element 1233 in its most basic form provides a logical ORfunction. Each drain terminal 1242, 1244 and 1246 and respective gate1248, 1250 and 1252 forms a field effect transistor in combination withthe common source terminal 1240 such that each transistor canindependently establish a conduction channel between its drain and thesource. This is an "ANY" or "OR" configuration.

The device 30a has a CMOS configuration, with one of the elements 1133,1233 having a first conductivity type, and the other of the elements1133, 1233 having a second conductivity type which is opposite to thefirst conductivity type.

More specifically, one of the elements 1133, 1233 will be N-channel(NMOS), and the other of the elements 1133, 1233 will be P-channel(PMOS). One of the elements 1133, 1233 will act as a pull-up element forthe output of the device 30a, whereas the other of the elements 1133,1233 will act as a pull-down element.

In order to minimize the area required on the substrate 32 by the device30a, the elements 1133, 1233 are preferably closely packed, with theperipheries 1134 and 1234 having a common edge. As illustrated, the edge1134-3 of the element 1133 is common with the edge 1234-3 of the element1233 such that the device has a quadrilateral or "diamond" shape.

The gates 1152, 1248 and 1148, 1252 are integrally formed, and extendacross the inactive areas 1138 and 1238. An electrical conductor 1253extends through the inactive areas 1138 and 1238 adjacent to the edges1134-1 and 1234-1 of the elements 1133 and 1233 respectively, andconnects the gate 1150 to the gate 1250. The gates 1248, 1250 and 1252of the ANY element 1233 are thereby electrically connected to the gates1152, 1150 and 1148 of the ALL element 1133 respectively.

A gate terminal 1154 which constitutes a common input terminal the gates1148 and 1252 is formed in the inactive area 1238 of the ALL element1233 adjacent to the edge 1234-2. A gate terminal 1156 which constitutesa common input terminal for the gates 1150 and 1250 is formed in theinactive area 1138 of the ALL element adjacent to the vertex 1134-4. Agate terminal 1158 which constitutes a common input terminal for thegates 1152 and 1248 is formed in the inactive area 1138 adjacent to theedge 1134-3.

It will be noted that the locations of the gate terminals 1154, 1156 and1158 are exemplary, and that the gate terminals can be located atdifferent points in the device in accordance with the requirements of aparticular design or application.

The inputs of the ALL element 1133 and the ANY element 1233 are therebyrespectively interconnected. As will be described below, the outputs ofthe ALL element 1133 and the ANY element 1233 are also interconnected toprovide a desired functionality.

A CMOS NAND gate 1260 based on the device 30a is illustrated in FIG. 49.The device 30a is shown in simplified form for clarity of illustration,with only the triangular peripheries of the elements 1133 and 1233 andtheir terminals included in the drawing. The terminals 1242 and 1246 arenot explicitly illustrated, and are assumed to be electrically connectedto the terminal 1244.

Input signals A, B and C are applied to the gate terminals 1158, 1154and 1156 respectively. A logically high signal or potential will beassumed to be substantially equal to V_(DD), and a logically low signalwill be assumed to be substantially equal to ground, with V_(DD) beingmore positive than ground.

The active area 1236 of the ANY element 1233 is N-type to provide PMOSoperation. The central terminal 1240 is connected to V_(DD), whereas anoutput signal OUT is taken at the interconnected drain terminals 1242,1244 and 1246.

Any low input will establish a conductive channel between the terminals1242, 1244 and 1246 and the central terminal 1240, thereby connectingthe output to V_(DD) and producing a high output signal OUT. When all ofthe inputs are high, the ANY element 1233 is turned off and theterminals 1242, 1244 and 1246 float.

The ANY element 1233 thereby functions as a pull-up element of the CMOSNAND gate 1260, in which any low input produces a high output.

The active area 1136 of the ALL element 1133 is P-type to provide NMOSoperation. The source terminal 1140 is connected to ground, and thedrain terminal 1142 is connected to the terminals 1242, 1244 and 1246 ofthe ANY element 1233 to provide a common output.

When any of the inputs are low, the ALL element 1133 is turned off andthe terminal 1142 will float. If all of the inputs are high, aconductive channel will be established between the terminals 1140 and1142 to connect the output to ground and produce a logically low output.

The ANY element 1133 therefore functions as a pull-down element of theCMOS NAND gate 1260, such that any low input produces a high output, andthe output is low in response to all inputs being high.

A CMOS AND gate 1270 incorporating the device 30a is illustrated in FIG.50. The active area 1236 of the ANY element 1233 is N-type to providePMOS FET operation, and the terminals 1242, 1244 and 1246 are connectedto ground. The output signal OUT appears at the central terminal 1240.

Due to the PMOS configuration of the ANY element 1233 in the AND gate1270, a logically low input signal A, B or C will establish a conductivechannel between the terminals 1242, 1244 and 1246 respectively and thecentral terminal 1240. This connects the output to ground. When all ofthe inputs are high, the ANY element 1233 is turned off, and theterminal 1240 floats.

Thus, any low input will produce a low output, and the ANY element 1233acts as a pull-down element of the CMOS AND gate 1270.

The active area 1136 of the ALL element 1133 is P-type to provide NMOSFET operation. The drain terminal 1142 is connected to V_(DD), and theterminal 1140 is connected to the terminal 1240 of the ANY element 1233to provide a common output OUT.

With any logically low input signal A, B and C applied to the gateterminal 1154, 1156 or 1158 respectively, the ALL element 1133 will beturned off and the terminal 1140 will float.

Since the ALL element 1133 provides NMOS operation in the configurationof FIG. 50, positive inputs to all of the gate terminals 1154, 1156 and1158 will establish a conductive channel between the terminals 1140 and1242. The entire channel will be enhanced, thereby connecting the sourceterminal 1140 to the potential V_(DD) through the drain terminal 1142 toproduce a logically high output.

In this manner, the ALL element 1133 acts as a pull-up element of theAND gate 1270, such that the gate 1270 produces a logically high outputwhen all of the inputs are high, and a logically low output when any ofthe inputs are low.

A NOR gate 1280 incorporating the device 30a is illustrated in FIG. 51,in which the active area 1236 of the ANY element 1233 is P-type toprovide NMOS operation. The central terminal 1240 is connected toground, and the terminals 1242, 1244 and 1246 are connected to providean output.

When all of the inputs are low, the ANY element 1233 is turned off andthe terminals 1242, 1244 and 1246 will float. If any of the inputs ishigh, a conductive channel will be established between the respectiveterminals 1242, 1244 and 1246 and the central terminal 1240 to connectthe terminals 1242, 1244 and 1246 and thereby the output to ground toproduce a logically low output.

In this manner, the ANY element 1233 acts as a pull-down element of theCMOS NOR gate 1280, with the output OUT being low if any or all inputsare high.

The active area 1136 of the ALL element 1133 is N-type to provide PMOSoperation. The source terminal 1140 is connected to V_(DD), whereas thedrain terminal 1142 is connected to the output OUT.

All low inputs will establish a conductive channel between the terminals1140 and 1142, thereby connecting the output to V_(DD) and producing ahigh output. When any of the inputs are high, the ALL element 1133 isturned off and the terminal 1142 floats.

Thus, the NOR configuration is provided, in which the ALL element 1133acts as a pull-up element, any high input produces a low output, and theoutput is high in response to all inputs being low.

A CMOS OR gate 1290 based on the device 30a is illustrated in FIG. 52.The active area 1236 of the ANY element 1233 is P-type to provide NMOSFET operation. The terminals 1242, 1244 and 1246 are connected toV_(DD), whereas the terminal 40 is connected to provide an output.

With all logically low input signals applied to the gate terminals 1254,1256 and 1258 respectively, the ANY element 1233 will be turned off andthe terminals 1242, 1244 and 1266 will float.

Since the device 30a provides NMOS operation in the configuration ofFIG. 52, a positive input to any of the gate terminals 1254, 1256 and1258 will establish a conductive channel between the terminals 1242,1244 and 1246 respectively and the central terminal 1240. Any one ofthese channels will connect the central terminal 1240 to the potentialV_(DD) to produce a logically high output.

In this manner, the ANY element 1233 acts as a pull-up element of the ORgate 1290, and the output OUT is logically high when any or all of theinputs is high.

The active area 1136 of the ANY element 1133 is N-type to provide PMOSFET operation. The drain terminal 1142 is connected to ground, and thesource terminal 1140 is connected to provide an output.

Due to the PMOS configuration of the ALL element 1133 in the OR gate1290, all of the input signals must be logically low to establish aconductive channel between the terminals 1140 and 1142. This connectsthe output to ground.

Thus, the ANY element 1133 acts as a pull-down element in the CMOS ORgate 1290, and all low inputs will produce a low output.

The device 30a is illustrated as having three inputs, which is ideallysuited to the hexagonal device shape. However, it is within the scope ofthe invention to provide a gate device having one or two inputs. Adevice with one input can be used as a buffer or an inverter.

The device 30a can be configured without modification to operate as ifit had one or two, rather than three inputs. For example, if it isdesired to operate the NAND gate 1260 of FIG. 49 with only two inputs,the gate terminal 1158 can be connected to V_(DD) and the two inputsapplied to the gate terminals 1154 and 1156. The NOR gate of FIG. 51 canbe adapted to provide a two input configuration by connecting the gateterminal 1158 to ground and applying the two inputs to the gateterminals 1154 and 1156.

It is also within the scope of the invention to modify the device 30a tohave only one or two inputs by physically omitting one or two of thegates 1148, 1150 and 1152 and respective terminals 1142, 1144, 1146 and1154, 1156, 1158.

In the illustrated example, the terminals 1242, 1244, 1246 and 1142 areinterconnected internally as illustrated in FIG. 49. Conductors 1330a,1336 and 1338 which extend in the e₁ direction (see FIG. 8) are providedfor connection of the terminals 1240, 1244 and 1140 respectively.Conductors 1332, 1334 and 1340 which extend in the directions e₁, e₂ ande₃ are provided for connection of the terminals 1158, 1156 and 1154respectively. The conductors 1332, 1334 and 1340, which carry the inputsignals, are preferably formed in different conductor layers.

For example, FIG. 53 illustrates a modified CMOS NAND gate 1260' basedon a device 30a' which differs from the NAND gate 1260 of FIG. 49 inthat the source and drain terminals of the ANY element 1233 are reversedrelative to each other.

In this embodiment of the invention, the terminals 1242, 1244 and 1246constitute sources and are connected to V_(DD), whereas the centerterminal 1240 constitutes the drain and is connected to the output inparallel with the terminal 1142 of the ALL element 1133.

Although not explicitly illustrated, this modification is equallyapplicable to all other embodiments of the invention.

FIGS. 54, 55 and 56 illustrate how the connections of the device 30a canbe changed to provide a different logical function. In an AND/OR gate1200b, the central terminal 1240 of the ANY element 1233 is not used,and can be physically omitted if desired. The ANY element 1233 is PMOS,whereas the ALL element 1133 is NMOS. The terminals 1244 and 1246 of theare connected to V_(DD), and the output signal OUT appears at theterminal 1242. The terminals 1140 and 1142 of the ALL element 1133 areconnected to ground. An additional terminal 1202 is provided between thegates 1150 and 1152.

The gate 1200b provides the logical function

A+(B*C)

As illustrated in the equivalent circuit diagram of FIG. 55, the inputsB and C are applied to inverting inputs of an OR gate 1204, the outputof which is applied to a non-inverting input of an AND gate 1206. Theinput A is applied to an inverting input of the AND gate 1206, wherebythe output of the AND gate 1206 is

A+(B*C)

Referring to FIG. 54, the ANY element 1233 functions as the pull-upelement of the gate 1200b. Since the gate 1248 is in front of theterminal 1242, a logically low signal A must be applied to the gateterminal 1158 to enhance the channel under the gate 1248 and connect theterminal 1242 to either the gate 1250 or the gate 1252. This providesthe functionality of the AND gate 1206.

Since both terminals 1244 and 1246 are connected to V_(DD), a logicallylow signal B or C applied to the gate terminal 1154 or 1156 will enhancethe channel under the gate 1250 and 1252 respectively and establish aconductive path from V_(DD) to the gate 1248.

Thus, the output OUT will be pulled high if the input A and either ofthe inputs B and C are low. If the input A or either of the inputs B andC is high, no conductive path will be established between V_(DD) and theoutput at the terminal 1242, and the terminal 1242 will float.

The ALL element 1133 functions as the pull-down element of the gate1200b. Since the gate 1152 is disposed between the grounded terminal1142 and the terminal 1202 which is connected to the output, a highsignal A applied to the gate 1152 will enhance the channel under thegate 1152 and connect the output terminal 1202 to the terminal 1142 andthereby to ground. This provides the functionality of the AND gate 1206.

Since both gates 1148 and 1150 are disposed between the terminal 1140and the terminal 1202, high signals B and C must be applied to bothgates 1148 and 1150 to connect the terminal 1202 to the terminal 1140and thereby to ground. This provides the functionality of the OR gate1204.

Thus, the output OUT will be pulled low if the input A and/or bothinputs B and C are high, and the terminal 1202 will float if the input Aand either of the inputs B and C are low.

FIG. 56 illustrates the gate 1200b as represented by equivalentfield-effect transistors. PMOS transistors 1208, 1210 and 1212 representthe portions of the gate 1200b corresponding to functionality providedby the gates 1252, 1250 and 1248 and respectively. NMOS transistors1214, 1216 and 1218 represent the portions of the gate 1200bcorresponding to functionality provided by the gates 1152, 1148 and 1150respectively.

Triangular OR Gate Device

A semiconductor gate device for a microelectronic integrated circuit isdesignated by the reference numeral 30b and illustrated in FIG. 57. Thedevice 30b, in its basic form shown in this example, provides a logicalOR function, but can be adapted to provide a logical NOR, AND, NAND orother logical function as will be described below.

The gate device 30b is formed on a substrate 32, and has a triangularperiphery 34 including first to third edges 34-1, 34-2 and 34-3, andfirst to third vertices 34-4, 34-5 and 34-6 respectively in theillustrated arrangement. A triangular semiconductor active area 36 isformed within the periphery 34, and an inactive area 38 is definedbetween the active area 36 and the periphery 34.

The device 30b comprises a central electrically conductive electrode orterminal 40 which functions as a Field-Effect-Transistor (FET) sourceterminal, and first, second and third electrodes or terminals 42, 44 and46 respectively that are formed in the active area 36 adjacent to thefirst, second and third vertices 34-4, 34-5 and 34-6 respectively.

The terminals 42, 44 and 46 function as FET drain terminals, and arepreferably interconnected for operation. Although one each of theterminals 42, 44 and 46 is illustrated in the drawing, it is within thescope of the invention to provide two or more each of the terminals 42,44 and 46.

The device 30b further comprises first, second and third gates 48, 50and 52 that are formed between the first, second and third terminals 42,44 and 46 respectively and the central terminal 40. The gates 48, 50 and52 are preferably insulated gates, each including a layer of insulatingoxide with a layer of conductive material (metal or doped polysilicon)formed over the oxide in a Metal-Oxide-Semiconductor (MOS)configuration. First to third gate electrodes or terminals 54, 56 and 58are formed in the inactive area 38 adjacent to the triangular edges34-1, 34-2 and 34-3, and are electrically connected to the gates 48, 50and 52 respectively. It will be noted that the locations of the gateterminals 54, 56 and 58 are exemplary, and that the gate terminals canbe located at different points in the device in accordance with therequirements of a particular design or application.

In order to provide effective source-drain electrical isolation, theopposite end portions of each of the gates 48, 50 and 52 extend into theinactive area 38.

The device 30b, in its most basic form illustrated in this example,provides a logical OR function. Each drain terminal 42, 44 and 46 andrespective gate 48, 50 and 52 forms a field effect transistor incombination with the common source terminal 40 such that each transistorcan independently establish a conduction channel between its drain andthe source. This is an "any" or "OR" configuration.

An OR gate 60 based on the device 30b is illustrated in FIG. 58. Thedevice 30b is shown in simplified form for clarity of illustration, withonly the triangular periphery 34 and terminals 40, 44, 54, 56 and 58included in the drawing. The terminals 42 and 46 are not explicitlyillustrated, and are assumed to be electrically connected to theterminal 44. Input signals A, B and C are applied to the gate terminals54, 56 and 58 respectively, and an output signal OUT is taken at thecentral or source terminal 40.

In the OR gate 60 of FIG. 58, the active area 36 of the device 30b isP-type to provide NMOS FET operation. The terminals 42, 44 and 46 areconnected to an electrical potential V_(DD) which is more positive thanground. The terminal 40 is connected to ground through a pull-downresistor 62.

A logically high signal will be assumed to be substantially equal toV_(DD), and a logically low signal will be assumed to be substantiallyequal to ground. With all logically low input signals A, B and C appliedto the gate terminals 54, 56 and 58 respectively, the device 30b will beturned off and the resistor 62 will pull the output low (to ground).

Since the device 30b provides NMOS operation in the configuration ofFIG. 58, a positive input to any of the gate terminals 54, 56 and 58will establish a conductive channel between the terminals 42, 44 and 46respectively and the central terminal 40. Any one of these channels willconnect the central terminal 40 to the potential V_(DD) to produce alogically high output. In this manner, the OR gate 60 produces alogically high output when any or all of the inputs is high.

FIG. 59 illustrates the device 30b connected in circuit to function as aNOR gate 64. In this case also, the active area 36 of the device 30b isP-type to provide NMOS operation. The central terminal 40 is connectedto ground, and the terminals 42, 44 and 46 are connected to V_(DD)through a pull-up resistor 66. The output signal OUT appears at theterminals 42, 44 and 46.

When all of the inputs are low, the device 30b is turned off and theoutput will be pulled to V_(DD) by the pull-up resistor 66 to produce alogically high output. If any of the inputs is high, a conductivechannel will be established between the respective terminals 42, 44 and46 and the central terminal 40 to connect the terminals 42, 44 and 46and thereby the output to ground to produce a logically low output. Inthis manner, the output signal OUT will be high if all inputs are low,and low if any or all inputs are high to produce the NOR function.

An AND gate 70 incorporating the device 30b is illustrated in FIG. 60.In the AND gate configuration, the active area 36 is N-type to providePMOS FET operation, and the terminals 42, 44 and 46 are connected toground. The central terminal 40 is connected to V_(DD) through a pull-upresistor 72, and the output is taken at the terminal 40.

Due to the PMOS configuration of the device 30b in the AND gate 70, alogically low input signal applied to input points A, B or C willestablish a conductive channel between the terminals 42, 44 and 46respectively and the central terminal 40. This connects the output toground. Thus, any low input will produce a low output.

When all of the inputs are high, the device 30b is turned off, and theoutput is pulled high by the pull-up resistor 72. Thus, the desired ANDfunction is provided.

A NAND gate 74 incorporating the device 30b is illustrated in FIG. 61,in which the active area 36 is N-type to provide PMOS operation. Thecentral terminal 40 is connected to V_(DD), whereas the terminals 42, 44and 46 are connected to ground through a pull-down resistor 76. Theoutput is taken at the terminals 42, 44 and 46.

Any low input will establish a conductive channel between the terminals42, 44 and 46 and the central terminal 40, thereby connecting the outputto V_(DD) and producing a high output. When all of the inputs are high,the device 30b is turned off and the output is pulled to ground by theresistor 76. Thus, the NAND configuration is provided, in which any lowinput produces a high output, and the output is low in response to allinputs being high.

The device 30b is illustrated as having three inputs, which is ideallysuited to the triangular device shape. However, it is within the scopeof the invention to provide a gate device having one or two inputs. Adevice with one input can be used as a buffer or an inverter.

The device 30b can be configured without modification to operate as ifit had one or two, rather than three inputs. For example, if it isdesired to operate the OR gate 60 of FIG. 58 with only two inputs, thegate terminal 58 can be grounded and the two inputs applied to the gateterminals 54 and 56. The AND gate 70 of FIG. 60 can be adapted toprovide a two input configuration by connecting the gate terminal 58 toV_(DD) and applying the two inputs to the gate terminals 54 and 56.

It is also within the scope of the invention to modify the device 30b tohave only one or two inputs by physically omitting one or two of thegates 48, 50 and 52 and respective terminals 42, 44, 46 and 54, 56, 58.

An example of the device 30b as being interconnected using the hexagonalrouting arrangement of FIG. 8 is illustrated in FIG. 62. It will beunderstood that the particular interconnect directions shown in thedrawing are selected arbitrarily for illustrative purposes, and are notin any way limitative of the scope of the invention. In general, any ofthe wiring directions can be utilized to interconnect any of theelements of the device 30b.

In the illustrated example shown in FIG. 62, a conductor 1160 whichextends in the direction e₁ (see FIG. 8) is provided for interconnectingthe terminals 42 and 46. Conductors 1162 and 1164 which also extend inthe direction e₁ are provided for interconnection of the centralterminals 44 and 40 respectively.

A conductor 1166 which extends in the direction e₁ is provided forinterconnection of the gate terminal 54 for the input A. A conductor1168 which extends in the direction e₂ provides interconnection of thegate terminal 56 for the input B, whereas a conductor 1170 which extendsin the direction e₃ provides interconnection of the gate terminal 58 forthe input C.

The conductors 1166, 1168 and 1170 are preferably provided in threeseparate wiring layers respectively. The conductors 1160, 1162 and 1164are preferably provided in another wiring layer or conductive plane.

The invention is not limited to the particular arrangement of conductorsillustrated in FIG. 62. For example, the conductors 1160, 1162 and 1164can also extend in three directions which are rotated by 60° relative toeach other. In such an arrangement, the conductor 1160 can extend in thedirection e₁ together with the conductor 1166, the conductor 1162 canextend in the direction e₂ together with the conductor 1168, and theconductor 1164 can extend in the direction e₃ together with theconductor 1170.

FIG. 63 illustrates a microelectronic integrated circuit 1180 accordingto the present invention comprising a semiconductor substrate 1182 onwhich a plurality of the devices 30b are formed in a closely packedtriangular arrangement. Further shown are a few illustrative examples ofinterconnection of the devices using the conductors 1160, 1162, 1164,1166, 1168 and 1170 which extend in the three directions e₁, e₂ and e₃.

It will be noted that six closely packed devices 30b define a hexagonalshape having a periphery 1184. This relationship can be used within thescope of the invention to provide unit cells having hexagonal shapesdefined by closely packed triangles, with internal structures similar toor different from that those which are explicitly described andillustrated. In such an arrangement, the hexagon can be considered to bethe basic building block.

FIG. 64 illustrates a modified OR gate 60' based on the device 30b whichdiffers from the OR gate 60 of FIG. 58 in that the source and drainterminals of the device 30b are reversed relative to each other.

In this embodiment of the invention, the terminals 42, 44 and 46constitute sources and are connected to provide the output across thepull-down resistor 62, whereas the center terminal 40 constitutes thedrain and is connected to V_(DD).

The operation of the OR gate 60' is otherwise similar to that of the ORgate 60. Although not explicitly illustrated, this modification isequally applicable to all other embodiments of the invention.

FIGS. 65, 66 and 67 illustrate how the connections of the device 30b canbe changed to provide a different logical function. In an AND/OR gate1200c, the central terminal 40 of the device 30b is not used, and can bephysically omitted if desired.

In the gate 1200c, the second and third terminals 44 and 46 areconnected to V_(DD), and the output signal OUT appears at the firstterminal 42 which is connected to ground through a pull-down resistor1202.

The gate 1200c provides the logical function A(B+C). As illustrated inthe equivalent circuit diagram of FIG. 66, the inputs B and C areapplied to inputs of an OR gate 1204, the output of which is applied toan input of an AND gate 1206. The input A is applied to another input ofthe AND gate 1206, whereby the output of the AND gate 1206 is A(B+C).

Since the first gate 48 is disposed in front of the first terminal 42which provides the output OUT, a high input must be applied to the firstgate terminal 54 to enhance the channel under the gate 48 to allowcurrent to flow to the first terminal 42 from any other part of thedevice 30b. This provides the function of the AND gate 1206 of FIG. 66.

Since both the second and third terminals 44 and 46 are connected toV_(DD), enhancement of either of the channels under the second and thirdgates 50 and 52 will establish a conductive path between V_(DD) and thefirst gate 48. Thus, a logically high signal applied to either of thesecond and third gate terminals 56 and 58 will connect V_(DD) to thegate 48. This provides the function of the OR gate 1204 of FIG. 66.

In this manner, the output of the gate 1200c will be logically high ifthe input A and either of the inputs B or C is logically high, and theoutput of the gate 1200c will be logically low if the input A is lowand/or if both of the inputs B and C are low.

The gate 1200c is illustrated in the form of equivalent FET transistorsin FIG. 67. The functionality of an FET 1210 is provided by the firstterminal 42 and the first gate 48 as shown in FIG. 65. The functionalityof an FET 1212 is provided by the second terminal 44 and second gate 50,whereas the functionality of an FET 1214 is provided by the thirdterminal 46 and third gate 52.

Similar operation can be obtained by using the second terminal 44 or thethird terminal 46 as the output terminal, and connecting the otherterminals to V_(DD). The principle is that by connecting one of theterminals to the output, the respective gate can block current flow fromboth of the other terminals, whereas the other two gates can blockcurrent flow only from their own respective terminals.

It is further within the scope of the invention to connect two terminalsto the output as illustrated in FIG. 68. In a gate 1210, the firstterminal 42 and the third terminal 46 are connected to the output,whereas the second terminal 44 is connected to V_(DD).

The gate 1210 provides the logical function B(A+C), because the secondgate 50 can block current flow from V_(DD) to the output, whereas eitherof the gates 48 and 52 can establish a conductive path between thesecond gate 50 and the output.

Space in the present triangular OR gate device is used most efficientlyin the illustrated configuration, in which the terminals are disposedadjacent to the apices of the triangle and the gate terminals aredisposed adjacent to the edges of the triangle.

However, the present invention is not so limited, and it is possible tolocate the terminals adjacent to the edges, and locate the gateterminals adjacent to the apices of the triangle. Other arrangements ofthe terminals, although not explicitly illustrated, are possible withinthe scope of the invention.

Alternative Embodiments Of Hexagonal Architecture

A preferred method of fabricating a microelectronic structure (such asan integrated circuit) in accordance with a combination of preferredtri-directional routing and hexagonal cell layout generally comprisessuperimposing a pattern of closely packed hexagons on a semiconductorsubstrate, and forming a plurality of microelectronic cells havingterminals on the substrate. Selected terminals are interconnected in apredetermined manner with a plurality of first, second and thirdelectrical conductors that extend in first, second and third differentdirections respectively. The first, second and third electricalconductors extend in directions parallel to the direction of lines thatpass through points defined by centers of the hexagons, and extendperpendicular to edges of the hexagons. While this is a preferredembodiment, it should be appreciated that the routing directions may bearbitrarily oriented with respect to the layout of the hexagonal shapedcells, these two aspects of the architecture being capable of existingindependently of each other.

In this manner, the electrical conductors extend in three directionsthat are angularly displaced from each other by 60°. However, analternative embodiment may include an implementation having a pluralityof conductors that extend in a plurality of directions that form anacute angle relative to each other.

In accordance with one aspect of the present invention, the centers ofthe hexagons 2030 as indicated at 2032 represent potential interconnectpoints for terminals of the cells. Electrical conductors forinterconnecting the points 2032 extend in three directions that makeangles of 60° relative to each other.

As will be described in detail below, the conductors that extend in thethree directions can be formed in three different layers, oralternatively the conductors that extend in two or three of thedirections can be formed in a single layer as long as they do not cross.

FIG. 73 illustrates a combination of a preferred tri-directional routing(having three layers of interconnect extending in three differentdirections angularly displaced from each other by 60 degrees) withclosely packed hexagonal shaped cells. The centers of the hexagons 2030or points 2032 are illustrated as all being potentially interconnectedby possible paths 2060 for conductors extending in the direction e₁,possible paths 2062 for conductors extending in the direction e₂ andpossible paths 2064 for conductors extending in the direction e₃.

FIG. 74 illustrates another desirable property of the present hexagonalrouting arrangement in that it provides substantially 100% equidistantconnectivity between adjacent cells (assuming the pins to be connectedare substantially centered, or similarly located), and it provides threedegrees of freedom for routing between neighboring cells.

As shown in the drawing, the distances between a center 2032a of ahexagon 2030a and centers 2032b, 2032c and 2032d of hexagons 2030b,2030c and 2030d that are adjacent to the hexagon 2030a are all equal toone in X-Y coordinates, or 2ε. Although not explicitly illustrated, thedistances between the center 2032a and the centers of the other hexagons2030 that are adjacent to the hexagon 2030a are also one.

In this manner, the centers of all hexagons 2030 that are adjacent to aparticular hexagon 2030 are all equidistant from the center of theparticular hexagon 2030, and the adjacent equidistant connectivity inthis example is substantially 100%.

In contrast, using conventional rectilinear routing as applied to thehexagonal cell arrangement of FIG. 74, the distance from a center 2032eof a hexagon 2030e to a center 2032h of an adjacent hexagon 2030h isone. However, the center 2032e must be connected to centers 2032f and2032g of hexagons 2030f and 2030g by rectilinear conductors 2080, 2082and 2084, 2086 respectively, each of the paths having a length of0.5+√3/2=1.37 which is greater than one.

FIG. 75 illustrates an alternative embodiment, in which electricalconductors extending in three directions for interconnecting terminalpoints are all provided in one routing layer. In this configuration, itis necessary that the conductors extending in different directions donot cross each other, as this would cause the crossing conductors to beshorted together.

In the illustrated example, cells have hexagonal shapes that correspondto the hexagons themselves, and each cell (hexagon) has one terminalcorresponding to its center or point.

More specifically, a microelectronic structure, preferably an integratedcircuit as indicated at 2090, comprises a substrate 2092 on which areformed hexagonal microelectronic cells 2094 having centers that (in thisexample) constitute terminals 2096 for interconnection with other cells2094. The terminals 2096 of selected cells are interconnected in apredetermined manner based on the netlist of the circuit 2090 by firstelectrical conductors 2098 that extend in the direction e₁ as describedwith reference to FIG. 8, second electrical conductors 2100 that extendin the direction e₂ and third electrical conductors 2102 that extend inthe direction e₃.

It will be noted that no two conductors extending in differentdirections cross each other in this example. If two conductors extendingin different directions are connected to a particular terminal 2096, theconductors are connected to each other.

The conductors 2098, 2100 and 2102 can be formed on the same layerproviding a single layer interconnect for the cells 2094, oralternatively the conductor layer can be electrically insulated byproviding an insulating layer between the interconnect and the cells.For example, the cells 2094 can be formed directly on the substrate2092, and an electrically insulating layer (not shown) of, for example,silicon dioxide, can be formed over the substrate 2092 and the cells2094. The conductors 2098, 2100 and 2102 may be then formed in a singlelayer over the insulating layer.

If the conductor layer is insulated from the cell layer, the conductors2098, 2100 and 2102 may be connected to the terminals 2096 byelectrically conductive feedthroughs or vias that extend through holes(not shown) in the insulating layer.

Alternatively, a plurality of metal layers may be provided, where eachsingle layer may include interconnections in a plurality of directionsangularly displaced from each other by 60 degrees.

Whereas the cells 2094 of FIG. 75 have the same hexagonal shape as thehexagons 2030 of FIG. 8, FIG. 76 illustrates an embodiment of theinvention in which the cells have shapes that are different from thehexagons 2030. In this case, the hexagons 2030 are not an actual part ofthe integrated circuit, but are superimposed on the circuit in animaginary pattern to define the points and directions for the hexagonalrouting conductors.

As viewed in FIG. 76, an integrated circuit 2110 comprises a substrate2112 on which a plurality of cells are formed. Each of the cells isformed within a single hexagon 2030, or within a cluster of adjacenthexagons 2030.

As shown, the circuit 2110 comprises a plurality of rectangular cells2114 having terminals 2116 disposed at the centers of respectivehexagons 2030. Each cell 2114 is formed within a single hexagon 2030 andhas a single terminal 2116.

Further illustrated is a circular cell 2118 having a center 2120. Thecell 2118 is preferably inscribed in the respective hexagon 2030 tomaximize the size of the cell 2118, but may be smaller if desired.

The integrated circuit 2110 further comprises a rectangular cell 2122that is disposed within a cluster consisting of two adjacent hexagons2030₁ and 2030₂. The cell 2122 has two terminals 2124 and 2126 locatedat the centers of the hexagons 2030₁ and 2030₂ respectively.

In general, as will be described in detail below, cells having terminalsthat are interconnected in accordance with the present hexagonal routingarrangement can have any shape, and can be formed in clusters comprisingany number of adjacent hexagons 2030.

The terminals 2116, 2120, 2124 and 2126 are interconnected in a desiredmanner by the electrical conductors 2098, 2100 and 2102 extending in thedirections e₁, e₂ and e₃ respectively as illustrated and described withreference to FIG. 75.

FIG. 77 illustrates another embodiment of the invention in which theelectrical conductors extending in two directions are formed in a firstlayer, whereas the electrical conductors extending in the thirddirection are formed in a second layer that is electrically insulatedfrom the first layer.

An integrated circuit 2130 comprises a substrate 2132 on which areformed a plurality of hexagonal shaped cells 2134 having terminals 2136.It will be noted, however, that the invention is not so limited, andthat the cells 2134 can have other shapes and can occupy more than onehexagon as described with reference to FIG. 76.

In this case, the electrical conductors 2098 that extend in thedirection e₁ and the conductors 2102 that extend in the direction e₃ areformed in a first layer, whereas the conductors 2100 that extend in thedirection e₂ are formed in the second layer. An electrically insulatinglayer that separates the two conductor layers, as well as an optionalinsulating layer that separates the conductor layers from the cells 2134on the substrate 2132, are not explicitly illustrated.

Any conductors 2098 and 2102 that are both connected to a particularterminal 2136 are thereby connected to each other. However, intermediateportions of conductors 2098, 2100 and 2102 that extend over particularterminals 2136 may or may not be connected to these terminals. If such aconductor is formed in a layer that is insulated from the cell layer andconnection is desired, such can be provided by a feedthrough asdescribed above.

FIG. 78 illustrates another embodiment in which the electricalconductors extending in the three directions are formed in three layersrespectively that are electrically insulated from each other. Anintegrated circuit 2140 comprises a substrate 2142 on which hexagonalcells 2144 having terminals 2146 are formed. Desired terminals 2146 areinterconnected by the conductors 2098, 2100 and 2102, intermediateportions of which may or may not be connected to underlying terminals2146 by feedthroughs as described above.

In the embodiment of FIG. 78, one of the layers of conductors 2098, 2100and 2102 can be formed on the cell layer, or all of the conductor layerscan be insulated from the cell layer.

As described above with reference to FIG. 76, a cell of any shape can beformed within a cluster of any number of adjacent hexagons 2030. Asillustrated in FIG. 79, a square cell 2150 is formed within a cluster2152 (as indicated in bold line) consisting of 22 adjacent hexagons2030. The cell has 18 terminals 2154 located at centers of thecorresponding hexagons.

Another advantageous feature of the present hexagonal routingarrangement is that cells of various shapes can be more closelyapproximated by clusters of hexagons than by rectangular shapes as inthe prior art.

FIG. 80 illustrates a circular cell 2160 that is formed within a cluster2162 of 19 adjacent hexagons 2030 and has 13 terminals 2164. Furtherillustrated is a square 2166 that circumscribes the cell 2160 to showhow the shape of the hexagonal cluster 2162 conforms more closely to thecell 2160 than does the square 2166.

FIG. 81 illustrates an irregular, generally gourd-shaped circular cell2170 that is formed within a cluster 2172 of 8 adjacent hexagons 2030and has 8 terminals 2174. Further illustrated is a rectangle 2176 thatcircumscribes the cell 2170 to show how the shape of the hexagonalcluster 2172 conforms more closely to the cell 2170 than does therectangle 2176.

FIG. 82 illustrates an integrated circuit 2180 comprising a substrate2182 on which are formed a plurality of cells 2184 similar to the cell2150 of FIG. 79. Each cell 2184 is formed within a cluster comprising aplurality of hexagons 2030. Although not explicitly illustrated,terminals of the cells 2184 are preferrably interconnected by electricalconductors extending in the three directions as described above.

The integrated circuit 2180 further comprises at least one, in theillustrated example three, electrical conductors 2186, 2188 and 2190that extend in the direction e₁ through the centers of hexagons 2030that are spaced between the upper and lower cells 2184. The conductors2186, 2188 and 2190 may constitute, for example, power, ground and clocksignal connections, and are connected, although not explicitlyillustrated, to terminals in the cells 2184 by conductors extending inthe directions e₂ and e₃.

The conductors 2186, 2188 and 2190 may be formed in the same layer asthe other conductors in the e₁ layer, or may alternatively be formedover the cell in another layer that is electrically insulated from boththe e₁ layer and the cell. It is further within the scope of theinvention to provide one or more of the conductors 2186, 2188 and 2190in the e₁ layer, and one or more of the other conductors 2186, 2188 and2190 in another layer.

Although one aspect of the present invention specifically relates toproviding a hexagonal routing arrangement including conductors extendingin three directions that are rotated by 60° from each other, oneembodiment of the invention does not preclude adding one or moreconductors in additional layers. In this regard, FIG. 82 furtherillustrates an additional electrical conductor 2192 that extends betweenthe left and right cells 2184 perpendicular to the direction e₁. Theconductor 2192 is formed in a fourth layer that is electricallyinsulated from the other three layers in order to prevent shorting theother conductors together.

FIG. 83 illustrates another integrated circuit 2180' embodying thepresent invention which is similar to the circuit 2180 of FIG. 82, andin which like elements are designated by the same reference numerals. Inthe circuit 2180', the upper and lower cells 2184 are staggered in thedirection e₁ to enable a conductor 2200 that extends in the e₂ directionand conductors 2202 and 2204 that extend in the e₃ direction to beprovided between the cells 2184 as illustrated. The conductors 2200,2202 and 2204 can be provided in the same layers as the other conductorsextending in the respective directions, or can be formed in separatelayers and insulated from the other layers.

FIGS. 79, 80 and 81 illustrate how various cells having any essentiallyarbitrary shape can be provided within a hexagonal architecture. FIGS.85 to 88 illustrate how megacells can be advantageously defined byclusters of hexagonal shaped cells. In the illustrated example, themegacells have serrated edges that tile well such that adjacent cellsfit together exactly, thereby eliminating spaces between adjacentmegacells and enabling substantially 100% utilization of space by thecells on the substrate.

For purposes of comparison, FIG. 84 illustrates a prior art integratedcircuit 2300 including a substrate 2302 on which are formed first andsecond rectangular cells 2304 and 2306, respectively, that share acommon edge or border 2308. The cells 2304 and 2306 are formed in aconventional rectangular arrangement and include interconnect pins orterminals 2310.

The rectilinear distances from an exemplary terminal 2310a torectangularly adjacent terminals 2310b, 2310c, 2310d and 2310e areequal. However, the rectilinear distances from the terminal 2310a todiagonally adjacent terminals 2310f, 2310g, 2310h and 2310i are longerthan the distances from the terminal 2310a to the rectangularly adjacentterminals 2310b, 2310c, 2310d and 2310e.

Assuming that the vertical and horizontal spacings between the terminals2310 are equal, the rectilinear distances from the terminal 2310a to thediagonally adjacent terminals 2310f, 2310g, 2310h and 2310i will betwice as long as the rectilinear distances between the terminal 2310a torectangularly adjacent terminals 2310b, 2310c, 2310d and 2310e.

For this reason, the adjacent equidistant connectivity of terminals inthe illustrated prior art rectilinear arrangement is 50%. This ratio maybe lower for connections to external terminals. For example, therectilinear distances from a terminal 2310j at an edge of the circuit2300 to diagonally adjacent external pins or terminals 2312b and 2312cis twice as long as to a rectangularly adjacent external terminal 2312a,such that the adjacent equidistant connectivity is 33.3%. It will benoted, however, that the distances from a terminal 2310k at a corner ofthe circuit 2300 to rectangularly adjacent external terminals 2312b and2312d on the adjacent edges that share the corner are equal.

In addition, the rectilinear distances between each terminal and itsdiagonally adjacent terminals is twice as long as between the terminaland its rectangularly adjacent terminals. If three directional routingwere applied to the arrangement of FIG. 84 such that diagonally adjacentterminals were connected by diagonal interconnects extending at 45°angles to the rectilinear directions, the lengths of the diagonalinterconnects would be √2=1.41 times longer than rectilinearinterconnects between rectangularly adjacent terminals.

FIG. 85 illustrates an integrated circuit 2320 according to analternative embodiment of the present invention including a substrate2322 on which are formed first and second cells 2324 and 2326respectively that are defined by clusters of hexagons 2327 and share acommon edge or border 2328 having a serrated shape. The cells 2324 and2326 include interconnect pins or terminals 2330 that are located in theillustrated example at the centers of the hexagons 2327.

The distances from a terminal 2330a to all of the six adjacent terminals2330b, 2330c, 2330d, 2330e, 2330f and 2330g are equal in this example,providing 100% equidistant connectivity. Since each terminal 2330 hasadjacent equidistant connectivity to six terminals, as compared to fourterminals in the prior art arrangement of FIG. 84, in this example usinga hexagonal cell arrangement, an increase of 50% is provided in adjacentequidistant connectivity over the illustrated prior art example.

The 100% adjacent equidistant connectivity in accordance this embodimentmay also be valid for connections to external pins or terminals in someinstances. As illustrated, the distances between a terminal 2330h andtwo adjacent external terminals 2332a and 2332b above the upper edge ofthe cell 2324 are equal. Similarly, the distances between a terminal2330i and external terminals 2332c, 2332d and 2332e adjacent to theright edge of the cells 2324 and 2326 are equal.

FIG. 86 shows how hexagonal shaped cells may form generally rectangularmegacells in accordance with the illustrated example having serratededges defined by edges of hexagons.

The arrangement of FIG. 86 is advantageous for an application in whichcells are arranged in columns, such that the cells in each column havethe same width. The three directional coordinate has been rotatedcounterclockwise by 90° from the orientation of FIG. 8 such that the e₁direction is vertical.

As illustrated in FIG. 86, an integrated circuit 2340 comprises asubstrate 2342 on which are formed a plurality of microelectronic cells2344, each being defined by clusters of hexagons 2345. The cells 2344fit together perfectly such that adjacent serrated edges thereof arecongruent, enabling 100% utilization of space on the substrate with 100%adjacent equidistant connectivity between terminals.

The example of FIG. 86 includes four columns of cells 2344, althoughthis is merely exemplary. The columns can have equal width, or differentwidths as illustrated. The e₁ direction is parallel to the columndirection, thereby enabling power and ground busses to be easilyconnected to all of the cells in a particular column as indicated bylines 2346, 2348, 2350 and 2352.

In order to fit together congruently, adjacent edges of cells shouldhave opposite "geometric sense". For the purpose of the presentdisclosure, the term "geometric sense" is defined to mean that aserrated edge with one geometric sense, e.g. male, has a shape that isconjugate to a serrated edge with the opposite geometric sense, e.g.female. In colloquial terms, the male edge has "zigs" where the femaleedge has "zags", and vice-versa.

Using the line 2346 as a reference, for example, upper and lower edges2354a and 2354b of a cell 2344a are defined as having "female" and"male" geometric sense because the line 2346 passes through concave andconvex portions of the edges 2354a and 2354b respectively.

A cell 2344b has upper and lower male edges 2354c and 2354d because theline 2346 passes through convex portions thereof. An exemplary cell2344c having male and female upper and lower edges 2354e and 2354fthrough which the line 2352 passes respectively is also illustrated.

The male and female edges differ from each other only in that they areshifted horizontally by one cell pitch (S=√3/2=0.87) relative to eachother. In order for two cells to be vertically adjacent and joined atcongruent edges, their congruent edges must have opposite geometricsense. The same relation is true in the orthogonal direction. Ingeneral, a cell 2344 with four serrated edges can have 2⁴ =16combinations of edges.

Although an arrangement is illustrated in FIG. 86 in which the e₁direction is vertical to enable power and ground routing parallel to thecolumn direction, it is of course within the scope of the illustratedembodiment to rotate the coordinate system by 90° so that the e₁direction is horizontal and runs parallel to the row direction. Thiswould enable cells to be arranged in rows, rather than in columns asillustrated.

If cells are arranged in columns, they may have equal widths (withineach column) and can have equal or unequal heights. If cells arearranged in rows, they may have equal heights and can have equal orunequal widths.

An advantageous configuration using one aspect of the present inventionis one in which the cells are closely packed on the substrate with 100%space utilization, and the routing interconnects are provided in threelayers that are electrically insulated from each other and from thecells on the substrate. However, the invention is not necessarilylimited to this or any of the exemplary configurations that areexplicitly described and illustrated.

It is not necessary for all of the edges of a cell to be serrated anddefined by edges of hexagons. FIG. 87 illustrates an integrated circuit2360 comprising a substrate 2362 on which are formed cells 2364 havingupper and lower serrated edges as described above with reference to FIG.86. However, the cells 2364 have at least one vertical edge that isstraight and not defined by edges of hexagons 2365. For example, a cell2364a has a serrated left edge and a straight right edge, a cell 2364bhas straight right and left edges and a cell 2364c has a straight leftedge and a serrated right edge.

The number of possible edge configurations for the cells of FIG. 87 is2² =4 for cells 2364 having two straight edges, and 2³ =8 for cells 2364having one straight edge.

It is further not necessary for a cell to have any regular shape. FIG.88 illustrates an integrated circuit 2370 comprising a substrate 2372having cells 2374 formed thereon that have highly irregular shapes. Thecells 2374 are illustrated as being closely packed to provide 100% spaceutilization, although the scope of the invention includes providingspaces and/or routing tracks between cells.

Most of the illustrated cells 2374 have all of their edges defined byedges of hexagons. However, the circuit 2370 further comprises a cell2374a having a right edge 2376a that is not defined by edges of hexagons2375 and is not straight. The right edge 2376a of the cell 2374a iscongruent with the left edge of a cell 2374b, which has an irregularright edge 2376b that is congruent with the left edge of a cell 2374c.

The freeform cell capability of FIG. 88 can be advantageously utilizedin an application where a cell can be designed with a givenfunctionality but have a shape that is variable within specifiedparameters. If, for example, an initial placement of regularly shapedcells produces an unroutable design with irregularly shaped gapstherein, the freeform design can be employed to generate cells that canfill the gaps and provide the required functionality and routability.

FIG. 89 illustrates another integrated circuit 2380 which comprises asubstrate 2382 having a plurality of closely packed cells 2384 formedthereon. The cells 2384 are hexagonal in shape and have centers 2384a.

A three directional routing grid for the cells 2384 may be provided bysuperimposing a pattern of smaller hexagons 2386 having centers 2388 onthe substrate 2382, where in this example the centers 2388 definelocations for terminals of the cells 2384. In this example, the patternof small hexagons 2388 is aligned with the cells 2384 such that thecenters 2384a of the cells 2384 are coincident with centers 2388 of thehexagons 2386.

The small hexagons 2386 have dimensions that are integral fractions ofselected dimensions of the cells 2384. In the illustrated example, acircle 2390 that circumscribes one of the cells 2384 has a radius 2392that is three times the distance between the centers 2388 of adjacenthexagons 2386. However, the sizes of the cells 2384 can be related tothe sizes of the hexagons 2388 in different ways. For example, cells2394 and 2396 are illustrated that are circumscribed by circles (notshown) having radii that are equal to one and two times the distancebetween the centers 2388 of the small hexagons respectively. The sizerelationship between the cells 2384 and the hexagons 2386 can also bedefined by ratios of edge lengths, inscribed circles and otherdimensions in various combinations.

To facilitate the design of an integrated circuit, it is advantageous toprovide a library including sets of cells having the same functionalitybut different shapes. This enables a cell having the requiredfunctionality to be placed in slots of different shapes on a substrate.

Such a set 2400 is illustrated in FIG. 90, and comprises four cells2402, 2404, 2406 and 2408 having the same predetermined functionality.The cells 2402, 2404, 2406 and 2408 are generally rectangular in shape,and each have upper and lower serrated edges defined by edges of asuperimposed pattern of hexagons 2410, and straight left and rightedges. It will be noted that the cells 2402, 2404, 2406 and 2408 aredefined by different numbers of hexagons, and are not exactly the samesize.

The cell 2402 has female upper and lower edges as defined by a line2412. The cell 2404 has male upper and lower edges. The cell 2406 has amale upper edge and a lower female edge, whereas the cell 2408 has afemale upper edge and a male lower edge. The cells 2402 and 2404 aredefined by a first number of hexagons, whereas the cells 2406 and 2408are defined by a second number of hexagons that is different from thefirst number.

Since the cells 2402, 2404, 2406 and 2408 have only two serrated edges,the set comprises 2² =4 cells. A set of generally rectangular cellshaving four serrated edges would consist of 2⁴ =16 cells.

In the above description, the terms "rectangular routing," "rectilinearrouting," and "hexagonal routing" have been used interchangeably.

Alternative Floorplanning Methods

FIG. 98 is a flow diagram showing a process by which floor planning maybe accomplished. The input to the process is a circuit design to be laidout on an integrated circuit which has a number of functions and anumber of I/O points, for which the respective areas required may beestimated. In a first step 1504, the total area required for allfunctions (adjusted to allow some space for interconnectionstherebetween) in the design is estimated. In a next step 1504, the totalI/O area required by the design is estimated In a next step 1506, afunction area to I/O area ratio is determined. A next step 1508 comparesthis ratio to function area to I/O area ratios for shapes in a libraryof available shapes (such shapes may include parallelograms, trapezoids,greatly elongated rectangles, triangles, etc., as well as "normal"rectangular and square shapes), selects a shape with a similar ratio,and sizes it to have a suitably large functional area. In this example,variable size dies are assumed. If only fixed-size shapes are available,then this becomes an additional constraint in the selection process,i.e., the selected shape must be large enough to contain the laid outcircuit.) Optionally, this step may take into consideration externallyimposed constraints, such as package shape, known circuit topology,etc., whereby the choice may be weighted towards a particular selection.In a next step 1510, a flat or hierarchical floorplanning process (e.g.,U.S. Pat. No. 4,918,614, to Modarres et al., with modifications asnecessary) is completed. Upon completion of the floorplanning process(1510), the results of the process are examined (1512). If the process(1510) was successful and the results are acceptable (all externalconstraints 1520 are met) then the resultant layout is used for furtherprocessing 1514 of the integrated circuit. If not, then another step1516 re-examines the available shapes in the library 1530 and selectsanother shape, then repeats the floorplanning process 1510.

External constraints 1520 may be provided by the user to limit thechoices of shapes or to bias the choice towards a particular shapeselection. This may be driven by a pre-selection of an IC package whichwill only accept certain die shapes or a pre-selection of a die whichwill only accept certain cell or array shapes. Another type of externalconstraint may derive from known circuit characteristics. For example,digital multipliers consist mostly of a sum-of-products adder arraywhich naturally tends to take on a parallelogram shape. In this case, itmay be desirable to weight the choice of cell shape, array shape, or dieshape towards a similarly shaped parallelogram array or die, or towardsome other compatible shape.

A method of floorplanning with low aspect ratio partitioning may beadvantageously employed in connection with the present inventions. Aspart of laying out non-square cells or arrays (functional blocks), on adie, it becomes apparent that most die are often square or nearlysquare. A square has a 1:1 aspect ratio. It may require some effort toplace hexagonal, triangular, trapezoidal, or other non-square functionalblocks in what starts out as a square area. Hence, as part of thefloorplanning process, partitioning proceeds with the goal of creatinglow aspect ratio areas (sub-partitions) for placing these lowaspect-ratio functional blocks. In general, functions are easier toplace in an area which is more geometrically "regular".

It becomes evident that when a single partitioning line is made on asquare die (which has an aspect ratio of 1:1) that the resulting twosubpartitions of the square have aspect ratios which are higher thanthat of the square die. For example, if the square die is dividedexactly in half, partitions result which have an aspect ratio of 2:1.(It should be noted that for the purposes of this discussion, all aspectratios are defined as the greater dimension divided by the lesserdimension. Therefore an object which might otherwise be considered tohave an aspect ratio of 0.5:1 is still described as having an aspectratio of 2:1.) These resultant partitions, being elongated, are muchlike the case of a high aspect ratio "certain non-square" die. In otherwords, low aspect ratio partitioning is not limited to "certainnon-square" dies. (The moment you partition at all, a low aspect-rationdie or area exhibits high aspect ratio sub-partitions which requirepartitioning). "Aspect-ratio", however is a term which is ordinarilyassociated with rectangular objects. A more general approach is requiredto fit this partitioning scheme to non-rectangular cells or arrays.

An area may be considered to have its lowest aspect ration when it has alow periphery to area ratio. For example, a rectangle 4 units in lengthby 1 unit in width has an area of 4 square units and a periphery to arearatio of 10 units divided by 4 square units, or 8.5/unit. A squarehaving the same area has a periphery to area ratio of 8.5/unit. Ingeneral, the more "elongated" (or the less geometrically "regular") anarea becomes, the greater its periphery to area ratio. This sameprinciple may be applied to triangles, or to any other shape. Forexample, a right triangle having a 4 unit side on one side of the rightangle and a 1 unit side on the other side of the right angle has an areaof 2 square units. Its periphery to area ratio is approximately4.561/unit. However, an isosceles right triangle, also having an area of2 square units, but having a 2 unit side on each side of the rightangle, has a periphery to area ratio of 3.414/unit. Clearly, the firsttriangle is more "elongated" than the isosceles right triangle, andconsequently has a higher periphery to area ratio.

While choosing a cell shape with a high periphery to area ratio isdesirable where large number I/O interconnections are expected, theresultant irregular or elongated area of the cell should be partitionedto yield sub-partitions having the smallest periphery to area ratiospossible for floorplanning purposes.

FIG. 99 is a flow diagram showing the process of floorplanningincorporating partitioning for minimum aspect ratio sub-partitions. Forthis example, a hierarchical process similar to U.S. Pat. No. 4,918,614,to Modarres et al. (hereinafter sometimes referred to as "Modarres") isused. In a first step 1602 the top level of a hierarchical design isselected. In a next step 1604, all of the area in question is allocatedto the top level (design), and is selected as the current partition. Theonly function in the top level (the entire design) is selected as thecurrent function. Recall that a design consists of a hierarchy oflevels, each level consisting of one or more parent functions each ofwhich may have one or more child functions. Each child function may bethe parent of still another child function at the next hierarchicallevel. If a function has no children, then it is a terminal function.The lowest level of the hierarchy has only terminal functions, althoughterminal functions may occur at any level of a hierarchy. Note againthat the top level of the hierarchy has only one function (i.e., theentire design), whereas lower levels of the hierarchy will likely havemore functions.

A next step 1606 creates minimum aspect ratio (MAR) sub-partitionswithin the current partition by selecting one or more partitioning lineplacement(s) which yield sub-partitions which have the lowest peripheryto area ratio(s) possible.

As in Modarres, a pre-defined threshold value is used in a next step1608 to determine whether heuristic or exhaustive placement is to beused. If the number of child functions of the currently selectedfunction in this level is small enough (smaller than or equal to thethreshold value) then an exhaustive placement process 1610 is used. Ifthe number of child functions is great enough (greater than thethreshold value) that exhaustive placement would require evaluation oftoo many permutations, then a heuristic placement process 1612, asdescribed in Modarres or as described hereinabove, is used. Both ofthese placement processes (1610 and 1612), attempt to optimizedistribution of functions to partitions by seeking a minimum partitioncost factor (PCF), either of the type described in Modarres, or of thetype described hereinabove.

A next step 1614 determines whether all functions in this level havebeen processed (i.e., have been sub-partitioned and had their childfunctions allocated to the subpartitions). If not, a next step 1610selects another function (as yet un-processed) at this level as thecurrent function, selects the area allocated to the newly selectedfunction as the current partition, and goes back to the sub-partitioningstep 1606.

If all of the functions at this level have been processed, a next step1618 determines whether all levels of the hierarchy have been processed.If not, a next step 1620 selects the next lower level in the hierarchy,selects a function at that level as the current function, and selectsthe area occupied by that function as the current function, and returnsto the sub-partitioning step. If all levels have been processed, thenstep 1618 continues with the fabrication process 1622.

If the subpartitioning process 1606 is used to create more than twosub-partitions, then multi-partitioned floorplanning results, requiringmulti-partition partition cost factors, as described hereinabove. Insome cases, especially on highly elongated shapes, it may be desirableto use multi-partitioning to produce sub-partitions with lower aspectratios. It may also be advantageous to change the number ofsub-partitions created depending upon the number, relative size orconnectedness of functions to be placed. All of these techniques may beutilized.

Hexagonal Vias

FIG. 131 shows a top view of three wires 851, 852 and 853, each of whichis in one of three layers of metal, and the wires are to be connected bya via 850. A first wire 851 is in the first layer of metal M1. A secondwire 852 is in the second layer of metal M2. A third wire 853 is in thethird layer of metal M3. Because the wires 851, 852 and 853 are indifferent metal layers (which are insulated from each other), toestablish an electrical connection between them a via 850 must be cutthrough the intervening insulating layers.

In the tri-directional routing described herein, when three wires crossin this manner, the via 850 will have a hexagonal shape as shown in FIG.131. The hexagonal shape of the via 850 provides advantages. Certainfailure modes of vias are believe to relate to the area to peripheryratio of the via. A hexagonal shaped via 850 has a more favorable ratiothan a square or rectangular shaped via.

More specifically, as the periphery to internal area ratio increases, asa hex ratio is larger than a square or rectangle, the performance andcontrollability of vias, especially for filled vias which formelectrical contacts which are often stacked to connect multiple layers,are increased. Additionally, as the corners of any such via, orespecially a filled via contact, become more obtuse, better properties(including avoidance or minimization of corner effects of electricalfields, lower likelihood of corner cracking and greater stackingalignment capability) results.

Thus, as hexagonal shapes for vias as shown in FIG. 131 have advantagesover well known square or rectangular vias, the invention includesshapes having more obtuse angles and higher periphery to area ratiosthan a square, including pentagonal, hexagonal, septagonal, octagonaland other 5+ sided regular shapes as well as circular (i.e. made by theintersection of a large number of possible lines), or oval shaped androunded-corner regular shaped vias and filled vias and contacts, allhereby included in the term "hexagonal shape" of the via or contact.

Digital Systems

It is contemplated that the method and apparatus of the presentinvention may be utilized in system level products comprising singlechip modules (SCM) often including other electrical components (such ascapacitors, resistors, inductors, etc.); multi-chip modules (MCM) havingat least two integrated circuit die in the same or separate packages,with or without other electrical components; board level products (BLP)such as those having multiple integrated circuits on printed wiringboard(s) (PWB); and box level products (Boxes) which may include acombination of elements from the list of SCM, MCM, BLP and the like. Oneor more of such SCM, MCM, PWB or BLP's may act as, or be integrated intoa functional system or subsystem. The system level products contemplatedinclude digital data storage; security and surveillance systems, generalpurpose computers (such as personal computers, work stations, servers,mini computers, mainframe computers and super computers); digital audioand video compression and transmission; transportation vehicles (such asairplanes, trains, automobiles, helicopters, rockets, missiles, boats,submarines, and the like); subsystems utilized in such vehicles (such asnavigational positioning, i.e., Global Positioning System (GPS),navigational displays and controllers, hazard avoidance such as radarand sonar, fly by wire control, and digital engine control andmonitoring); entertainment systems (such as digital television andradio, digital cameras, audio and video recorders, compact disc players,digital tape, or the like); and communications (such as PBX, telephoneswitching, voice mail, auto attendant, network controllers, videoteleconferencing, digital data transmission (such as token ring,Ethernet, ATM or the like), and subsystems or subassemblies forinclusion or attachment to more complex system level products.

It is contemplated and within the scope of the present invention that avery large scale (VLSI) integrated circuit die may have a plurality offunctional core blocks at different locations on the die, and that oneor more of the functional core blocks of the die may be constructed inaccordance with the present invention. The die clock may be adjusted forthe slowest functional core block so as to maintain maximum dieoperating speed consistent with reliability and data integrity, whilethe clock speed may be increased (e.g. doubled) for functional blocksconstructed in accordance with the present invention.

It is also contemplated that the present invention may be utilized in alarge digital system requiring synchronous or asynchronous operation ata maximum reliable clock speed. Different subsystems of this system maybe located at diverse locations. An advantage of the present inventionis that the a digital system may always run at maximum speed for alloperating conditions without having to derate the system components forslow speed circuits because certain integrated circuits are notconstructed in accordance with the present invention.

The present invention may be implemented in a system in that the systemor a component of the system may incorporate microelectronic integratedcircuits which include in whole or in part one or more of the structuresdescribed herein or made by one or more of the methods described herein.

The present invention may be utilized to design or fabricate integratedcircuits incorporated into digital systems, and for taking fulladvantage of the speed and computational power of the integratedcircuits utilized in a digital system which are implemented insemiconductor die. As used herein, a digital system may include analogcircuits and other non-digital components. A digital system may comprisesingle chip modules (SCM) including other electrical components;multi-chip modules (MCM) having a plurality of integrated circuits, withor without other electrical components; board level products (BLP) suchas those having multiple integrated circuits on printed wiring board(s)(PWB); and box level products (BLP) integrated into a functional systemor subsystem. The system level products contemplated include digitaldata storage; security and surveillance systems, general purposecomputers (such as personal computers, work stations, servers, minicomputers, mainframe computers and super computers); digital audio andvideo compression and transmission; transportation vehicles such asairplanes, trains, automobiles, helicopters, rockets, missiles, boats,submarines, and the like; subsystems utilized in such vehicles (such asGPS navigation, navigational displays and controllers, hazard avoidancesuch as radar and sonar, fly by wire control, and digital engine controland monitoring); entertainment systems (such as television and radio,digital cameras, audio and video recorders, compact disc players,digital tape, and the like); and communications (such as telephonesincluding portable and cellular, PBX, telephone switching systems, voicemail, auto attendant, network controllers, video teleconferencing,digital data transmission such as token ring, Ethernet, ATM, or andlike).

Reducing the size of semiconductor devices based upon the disclosedarchitecture and improving the speed of circuits otherwise limited byprior art rectilinear architecture and routing methods. The performanceof the integrated circuits comprising parts of a digital system whichutilize the disclosed architecture will allow the design engineers toimplement a design based upon improved "worst-case" device parametersthan was heretofore required to insure reliability of conventionalrectilinear device designs over all operating conditions. This may beespecially significant in high speed systems or computation intensivesystems, such as digital data compression and communications systems,and the like.

The present invention may be effectively utilized in a complex digitalsystem. A plurality of semiconductor integrated circuits, one or more ofwhich are constructed in whole or in part in accordance with the presentinvention, are incorporated into a digital system. It is expected thatintegrated circuits having rectilinear architecture will be the slowestand must be operated at a slower system clock (lower frequency). Otherintegrated circuits of the system will not be limited in operating speedwhen those integrated circuits are inherently faster than the otherintegrated circuits because they are constructed in accordance with thepresent invention.

The present invention may be utilized to improve the range of reliableoperation of an integrated circuit by implementing the circuit design inan integrated circuit having a more reliable architecture improving thespeed or reducing crosstalk in applications in which the integratedcircuit may operate. Of course, matching of compatible integratedcircuits that must operate together so that all critical circuitsincorporate the preferred architecture of the present invention isdesirable.

When a system requires a certain operating speed, the criticalintegrated circuits may be constructed in accordance with the presentinvention so as to realize a maximum performance, or minimum size, forthe system. When the integrated circuits of the system are much fasterthan necessary for desired operation, integrated circuits constructed inaccordance with the present invention may be incorporated to improveyields, to reduce cost, or improve reliability of the system.

Referring now to FIG. 100, a schematic block diagram of an integratedcircuit system incorporating the present invention is illustrated. Anintegrated circuit system, generally represented by the numeral 700, maycomprise a data interface unit 708, a control unit 714, a power source712, analog circuits 710, and other system components (not illustrated)that connect to an integrated circuit 702 incorporating the presentinvention. The integrated circuit 702 has at least an area or cell 706incorporating hexagonal architecture or tri-directional routing inaccordance with the present invention.

Referring now to FIG. 101, a schematic block diagram of a digital systemaccording to the present invention is illustrated. The digital system701 is comprised of a plurality of integrated circuits 702, a systemclock 713, interface circuits 707, and a control unit 703. The digitalsystem 701 may optionally include analog circuits 709, it beingunderstood that the term "digital system" is intended to refer tosystems that have digital elements, but does not require that allelements of the system be digital. The integrated circuits 702 areinterconnected, typically, to perform functions such as, for example,computation, memory, digital video compression, digital signalprocessing, forward error correction, navigation and guidance, or othercomplex digital monitoring, control or computational functions. Althoughnot shown, the digital system may have connections to external elements,such as input-output, display, peripherial, and other components, aswell as other systems.

Integrated circuits 702 utilize structures constructed in accordancewith the present invention. Integrated circuit 711 does not necessarilyincorporate the architecture of the present invention, because not allof the integrated circuits may be critical to the operation of thesystem nor have too low an operating speed that may pose a problem.

The control unit 703 may be, for example, a programmable logic array(PLA), application specific integrated circuit (ASIC), microprocessorand program, or the like. If necessary, the system clock 713 may be setat a relatively low system clock frequency for a slower or performancelimited integrated circuit 711, and clock doubler circuits or the likemay be incorporated into integrated circuits 702 to provide higher clockspeeds for faster chips 702 to take advantage of features of the presentinvention.

Referring now to FIG. 102, a schematic diagram of a multiprocessorcomputer system incorporating the present invention is illustrated. Thedigital system 705 has more than one microprocessor 704a and 704b, andthe microprocessors 704a and 704b may be identical but it is notrequired. A memory 715, interface 716, and perpherial devices 717 arealso shown. The microprocessors 704a and 704b may be interconnected,typically, to perform high speed parallel computation.

The microprocessors 704a and 704b may include at least portions ofintegrated circuits incorporating the present invention. The memory 715may also include at least portions of integrated circuits incorporatingthe present invention. Not all of the integrated circuits may becritical to the operation of the system nor does a low operating speedfor every integrated circuit necessarily pose a problem, and thus it maynot be necessary to construct all such circuits in accordance with thepresent invention.

Referring to FIG. 103, a schematic block diagram of a complex digitalcomputer system is illustrated. The digital computer system 718comprises a central processing unit ("CPU") 719 which operates inconjunction with the following subsystems: random access memory ("RAM")720, video controller 721, connectivity interface 722, disk controller723, and input/output controller 724. The aforementioned subsystems areinterconnected with each other and the CPU 719 by a bus system 725.

The system 718 may utilize programmable clocks 726 and 727. The firstclock 726 is utilized with the CPU 719 and RAM 720. In the illustratedexample, the second clock 727 is utilized with the video controller 721,connectivity interface 722, disk controller 723, and input/outputcontroller 724. The first clock 726 may run at a faster speed than thesecond clock 727. Multiple system clocks running at different speedswith or without phase lock synchronization therebetween may be employed.Higher speed system clocks may be desirable to take advantage of higherperformance available from devices such as the CPU 719 and the RAM 720constructed in accordance with the present invention.

The first clock 726 and the second clock 727 may be programmed by clockcontrol 728 to run the system 718 at maximum reliable operating speedsconsistent with the improved subsystem performance which may beavailable as a result of employing circuits 719 and 720 constructed inaccordance with the present invention. Various external devices 729 maybe connected to the input/output controller 724 or the connectivityinterface 722.

Referring now to FIG. 104, a schematic block diagram of a large scaleintegrated circuit according to the present invention is illustrated.The large scale integrated circuit 730 is comprised of a functionallogic core 731, a hexagonal memory array 732, a first triangularmegafunction cell 734, a second triangular megafunction cell 735, arectilinear cell 736, and other circuits 733. The integrated circuit 730may utilize hexagonal, triangular, parallelogram, or diamond shapedcells or may use tri-directional routing in three metal layers forinterconnections on the die, or may use both. In the illustratedexample, tri-directional routing 737 is used in the area of the chip 730surrounding the hexagonal array 732 and triangular cells 734, 735.Rectilinear routing 738 may be used in the area of the chip 730surrounding the core 731 and circuit 733, particularly if the density ofthe interconnections is low in that area or the blocks 731 and 733interconnect in a way that makes rectilinear routing satisfactory oradvantageous. Typical applications for the large scale integratedcircuit 730 may be single package computer and control systems, digitalsignal processing engines, data compression engines, forward errorcorrection engines, and the like.

Referring to FIG. 105, a schematic block diagram of a digital cellulartelephone system is illustrated. The digital cellular telephone system740 comprises a transmitter 739, receiver 741, antenna 742, programmableradio frequency oscillator 743, digital encoder 744, digital decoder745, and a control unit 746. The digital encoder 744 and decoder 745 mayhave mostly common circuits, but are illustrated separately for clarity.Included on at least one of the encoder 744 and decoder 745 integratedcircuits comprising the digital logic is at least one integrated circuit(not illustrated) incorporating the present invention. In addition, thecontrol unit 746 may include an integrated circuit (not illustrated)incorporating the present invention.

Digital communications, both video and audio, requires manipulation ofanalog signals into digital signals representative of the respectiveanalog signals. The digital signal information is compressed in order toreduce the information bandwidth requirements of the digital telephonesystem 740, as is well known to those skilled in digital communications.The present invention allow optimal performance of the digitalinformation processing logic in a digital communication system such as acellular telephone, direct broadcast satellite television and the like.

Referring to FIG. 106, a schematic block diagram of a digitalentertainment system such as a digital television, CD video and audio,and direct broadcast satellite is illustrated. The digital entertainmentsystem 747 is becoming more prevalent and is creating new entertainmentfor both the consumer and provider. Use of real time high resolutionvideo and multiple channel stereo audio requires that the digitalcircuits have very high data throughput. The greater the resolution ofthe information being displayed the faster the digital circuits mustoperate. Very fast digital circuits have a cost premium, thisrestricting the demand of such systems with the consumer. The presentinvention allows less expensive digital circuits to perform thenecessary digital logic functions required of the new digitalentertainment systems without having to pay a premium. In addition,these digital circuits may operate more than was heretofore possible.

The entertainment system 747 may comprise a digital encoder 748, errorcorrection encoder 749, and modulator 750 at the transmission end of thesystem 747. The reception end of the system 747 may comprise ademodulator 751, error decode and correction 752, and digital decoder753. A control unit 754 controls the reception end and the transmissionend of the system 747.

The present inventions are thus applicable to any digital technologywhich includes integrated circuits in a digital system, or differentfunctional core blocks of a very large scale intergated circuit.Examples of digital systems that may benefit from the architecture andmethods of the present inventions have been briefly described by way ofexample, and not by way of limitation. The spirit and intent of thepresent inventions is to improve the operating speed capability andreliability of, and to reduce the size of, all digital systems from asingle semiconductor integrated circuit die to a complex multiple boxcomputing system.

As stated above, it will be understood that the terms "source" and"drain" which have been used in the above description in relation tofield effect transistors merely define opposite ends of a channel regionwhich is controlled by a voltage applied to a gate. The source and drainare interchangeable in that current may flow into either one and out ofthe other. Therefore, the terms "source" and "drain", and the relativepolarities of voltages applied thereto, which may be described in theexamples illustrated in the present specification, are arbitrary andreversible within the scope of the invention, and are not to beconsidered as limiting the invention to one or the other of the possibleconfigurations or polarities.

The embodiments of the present inventions described herein have beengiven only as examples in order to illustrate the disclosed inventions.Persons skilled in the art, after having the benefit of the disclosureset forth herein, will appreciate that modifications may be made in theexamples described and illustrated herein without departing from thescope of the present inventions. The inventions are not intended to belimited to the examples shown and described. The scope of the inventionsare defined by the scope of the properly construed claims appended tothis patent.

What is claimed is:
 1. A transistor having dynamically adjustablecharacteristics, comprising:a semiconductor substrate having a dopedregion forming a well therein; a Y-shaped gate electrode formed over thedoped region defining a first main transistor in the doped region and asecond control transistor in the doped region, the first and secondtransistors having the Y-shaped gate electrode as a common gateelectrode, the first transistor having a first source, the secondtransistor having a second source, the first and second transistorshaving a common drain, the first main transistor having an effectivechannel width; and, whereby the effective channel width of the firstmain transistor may be dynamically varied by changing a source-to-drainvoltage applied to the second control transistor.
 2. A transistor havingdynamically adjustable characteristics, comprising:a semiconductorsubstrate having a doped region forming a well therein; a Y-shaped gateelectrode formed over the doped region defining a first main transistorin the doped region and a second control transistor in the doped region,the first and second transistors having the Y-shaped gate electrode as acommon gate electrode, the first transistor having a first source, thesecond transistor having a second source, the first and secondtransistors having a common drain, the first main transistor having adrive current; and, whereby the drive current of the first maintransistor may be dynamically varied by changing a source-to-drainvoltage applied to the second control transistor.
 3. A device havingdynamically adjustable characteristics, comprising:a semiconductorsubstrate having a tri-ister structure fabricated thereon; the tri-isterstructure including a Y-shaped gate electrode formed over a doped regiondefining a first main transistor in the doped region and a secondcontrol transistor in the doped region, the first and second transistorshaving the Y-shaped gate electrode as a common gate electrode, the firsttransistor having a first source, the second transistor having a secondsource, the first and second transistors having a common drain, thefirst main transistor having a drive current; and, whereby the drivecurrent of the first main transistor may be dynamically varied bychanging a source-to-drain voltage applied to the second controltransistor.
 4. A transistor structure, comprising:a semiconductorsubstrate having a doped region; a generally Y-shaped gate electrodewhich is formed over and divides the doped region into a source region,a drain region and a control region; and control means for controlling acharacteristic of current flow between the source region and the drainregion by applying a corresponding control voltage to the controlregion.
 5. A structure as in claim 4, in which said characteristic is adrive current.
 6. A structure as in claim 4, in which saidcharacteristic is an effective width of a channel under a portion of thegate electrode which divides the source region from the drain region. 7.A structure as in claim 4, in which the gate electrode comprises threeradially extending sections which are substantially rotationallysymmetrical.
 8. A structure as in claim 4, in which the gate electrodecomprises three radially extending sections, with at least one of saidsections having a different width than another of said sections.
 9. Astructure as in claim 8, in which widths of said sections are selectedsuch that a value of current flowing from the source region to the drainregion is a multiple of current flowing from the source region to thecontrol region.
 10. A structure as in claim 8, in which widths of saidsections are selected such that a value of current flowing from thesource region to the drain region is a multiple of current flowing fromthe drain region to the control region.
 11. A structure as in claim 4,in which the control means selectively applies a first control voltageor a second control voltage to the control region which sets saidcharacteristic at a first value or a second value respectively, suchthat said first value is substantially twice said first value.
 12. Astructure as in claim 11, in which said characteristic is a drivecurrent.
 13. A structure as in claim 11, in which said characteristic isan effective width of a channel under a portion of the gate electrodewhich divides the source region from the drain region.
 14. A structureas in claim 4, in which the control voltage is selected such that acurrent flowing from the source region to the drain region issubstantially equal to a current flowing from the source region to thecontrol region.
 15. A structure as in claim 4, in which the controlvoltage is selected such that a current flowing from the source regionto the drain region is substantially equal to a current flowing from thedrain region to the control region.
 16. A structure as in claim 4, inwhich the control voltage has a value between a voltage in the sourceregion and a voltage in the drain region.
 17. A method of controlling atransistor structure, comprising the steps of:(a) providing a transistorstructure as including a semiconductor substrate having a doped region;and a generally Y-shaped gate electrode which is formed over and dividesthe doped region into a source region, a drain region and a controlregion; and (b) controlling a characteristic of current flow between thesource region and the drain region by applying a corresponding controlvoltage to the control region.
 18. A method as in claim 17, in whichsaid characteristic is a drive current.
 19. A method as in claim 17, inwhich said characteristic is an effective width of a channel under aportion of the gate electrode which divides the source region from thedrain region.
 20. A method as in claim 17, in which step (a) comprisesproviding the gate electrode as comprising three radially extendingsections which are substantially rotationally symmetrical.
 21. A methodas in claim 17, in which step (a) comprises providing the gate electrodeas comprising three radially extending sections, with at least one ofsaid sections having a different width than another of said sections.22. A method as in claim 21, in which widths of said sections areselected such that a value of current flowing from the source region tothe drain region is a multiple of current flowing from the source regionto the control region.
 23. A method as in claim 21, in which widths ofsaid sections are selected such that a value of current flowing from thesource region to the drain region is a multiple of current flowing fromthe drain region to the control region.
 24. A method as in claim 17, inwhich step (b) comprises selectively applying a first control voltage ora second control voltage to the control region which sets saidcharacteristic at a first value or a second value respectively, suchthat said first value is substantially twice said first value.
 25. Amethod as in claim 24, in which said characteristic is a drive current.26. A method as in claim 24, in which said characteristic is aneffective width of a channel under a portion of the gate electrode whichdivides the source region from the drain region.
 27. A method as inclaim 17, in which the control voltage is selected such that a currentflowing from the source region to the drain region is substantiallyequal to a current flowing from the source region to the control region.28. A method as in claim 17, in which the control voltage is selectedsuch that a current flowing from the source region to the drain regionis substantially equal to a current flowing from the drain region to thecontrol region.
 29. A method as in claim 17, in which the controlvoltage has a value between a voltage applied to the source region and avoltage applied to the drain region.
 30. An electronic system comprisinga microelectronic structure including a semiconductor substrate having atransistor formed thereon, and additional electronic devices that areoperatively connected to the microelectronic structure, the transistorcomprising:a doped region formed on the substrate; a generally Y-shapedgate electrode which is formed over and divides the doped region into asource region, a drain region and a control region; and control meansfor controlling a characteristic of current flow between the sourceregion and the drain region by applying a corresponding control voltageto the control region.
 31. A system as in claim 30, in which theadditional electronic devices are formed on the substrate andoperatively connected to the transistor.
 32. A system as in claim 30, inwhich the microelectronic structure comprises a Single-Chip Module(SCM).
 33. A system as in claim 30, comprising a Multi-Chip Module(MCM), the microelectronic structure being part of the MCM.
 34. A systemas in claim 30, further comprising a Board-Level Product (BLP) includinga circuit board on which the microelectronic structure is mounted.
 35. Asystem as in claim 30, further comprising a box level product includinga power supply for the microelectronic structure.
 36. A system as inclaim 30, in which said characteristic is a drive current.
 37. A systemas in claim 30, in which said characteristic is an effective width of achannel under a portion of the gate electrode which divides the sourceregion from the drain region.
 38. A system as in claim 37, in which thegate electrode comprises three radially extending sections which aresubstantially rotationally symmetrical.
 39. A system as in claim 30, inwhich the gate electrode comprises three radially extending sections,with at least one of said sections having a different width than anotherof said sections.
 40. A system as in claim 39, in which widths of saidsections are selected such that a value of current flowing from thesource region to the drain region is a multiple of current flowing fromthe source region to the control region.
 41. A system as in claim 39, inwhich widths of said sections are selected such that a value of currentflowing from the source region to the drain region is a multiple ofcurrent flowing from the drain region to the control region.
 42. Asystem as in claim 30, in which the control means selectively applies afirst control voltage or a second control voltage to the control regionwhich sets said characteristic at a first value or a second valuerespectively, such that said first value is substantially twice saidfirst value.
 43. A system as in claim 42, in which said characteristicis a drive current.
 44. A system as in claim 42, in which saidcharacteristic is an effective width of a channel under a portion of thegate electrode which divides the source region from the drain region.45. A system as in claim 30, in which the control voltage is selectedsuch that a current flowing from the source region to the drain regionis substantially equal to a current flowing from the source region tothe control region.
 46. A system as in claim 30, in which the controlvoltage is selected such that a current flowing from the source regionto the drain region is substantially equal to a current flowing from thedrain region to the control region.
 47. A system as in claim 30, inwhich the control voltage has a value between a voltage in the sourceregion and a voltage in the drain region.